Stuffed Flounder with Spinach and Feta Cheese

Ingredients (serves 4)

Use fresh or fully thawed flounder fillets about 4–6 oz each and roughly 1/4–1/2″ thick when possible; very thin pieces can be made into pockets or gently rolled. For the filling, plan for 6 oz fresh spinach (cooks down to ~1 cup), ¾–1 cup crumbled feta, and a binder like 2–3 tbsp panko or 2 tbsp cream cheese to hold it together without drying it out.

• 4 flounder fillets, 4–6 oz each
• 6 oz fresh spinach
• ¾–1 cup crumbled feta
• 2–3 tbsp panko (or 2 tbsp cream cheese)
• 1 tbsp olive oil, 1 tbsp lemon juice, 1 tsp lemon zest
• 1–2 cloves garlic, minced; salt and pepper
• 2 tbsp butter (optional), toothpicks, baking dish

Equipment and prep you’ll need

Have an instant-read thermometer, a skillet, a fine-mesh strainer or clean kitchen towel for squeezing spinach, a baking dish, and toothpicks or butcher’s twine ready. An instant-read thermometer is important because flounder is thin and easy to overcook; the only reliable doneness measure is the internal temp of 145°F (63°C).

A rimmed baking sheet or shallow baking dish lined with parchment makes cleanup simple and helps the fish brown evenly, while a skillet with a tight sear helps if you choose the sear+finish method. We also recommend having panko and a small bowl to adjust filling moisture during assembly.

Step-by-step directions

Prep the fish (butterfly, pocket, or trim)

Pat fillets dry and check for bones; use tweezers to remove any. For a pocket, slice along the thicker edge to make a shallow pouch without cutting through; for a roll, lay the fillet skin-side down (if skin-on) and trim so pieces are even. Recommended portion: a 4–6 oz fillet takes about 2–3 tbsp filling.

To butterfly a very thick fillet, slice horizontally almost through and open like a book; this is useful for very large flounder. When fillets vary, trim the thick end so each cooks evenly — an even thickness is the single best way to avoid overcooking while the stuffing reaches temp.

Make the filling (sauté, season, bind)

Sauté garlic in 1 tbsp olive oil for 30–45 seconds, add 6 oz fresh spinach and cook until wilted, about 1–2 minutes. Transfer to a fine-mesh strainer or clean towel, press and squeeze until mostly dry — aim for less than 1/4 cup of liquid drained per batch; excess water will make the filling soggy.

Mix the cooled, squeezed spinach with ¾–1 cup crumbled feta, 2–3 tbsp panko (or 2 tbsp cream cheese), lemon zest, 1 tbsp lemon juice, salt and pepper to taste. Taste a small spoonful and adjust lemon or salt — balance matters because feta is salty and lemon keeps the filling bright.

Stuff and secure

Spoon about 2–3 tbsp filling into each pocket or place a strip down the center for rolling; do not overstuff — too much filling prevents even cooking. Tuck ends, roll or fold the fillet, and secure with 2 toothpicks per roll or set seam-side down in the dish to self-seal. Chill for 10 minutes to let the binder set if you have time — it really helps the shape hold.

I learned the hard way to always squeeze the spinach thoroughly; the first time I skipped that step the filling released water in the oven and made the fish steam instead of brown. After that we always press the spinach until it’s nearly dry — it saves the whole dish.

Cook: bake vs sear + finish

Bake-only method: preheat oven to 375°F (190°C) and bake stuffed fillets for 12–18 minutes depending on thickness, or until internal temp reaches 145°F (63°C). Faster option: 400°F (205°C) for 10–12 minutes if fillets are thin and you refrain from overstuffing.

Sear+finish: heat 1 tbsp oil in a skillet, sear seam-side down for 1–2 minutes to get color, then transfer to a 375°F (190°C) oven for another 8–10 minutes. Always finish to 145°F (63°C) internally — the thermometer is faster and more reliable than visual cues on thin fish.

Resting and serving

Let the fish rest for 3–5 minutes after removing from the oven so the juices redistribute and the filling firms slightly. Remove toothpicks before serving and finish with a squeeze of lemon and a drizzle of melted butter or a simple pan sauce. Garnish with extra lemon zest or chopped parsley for color and freshness.

Exact timing & temperature chart

Use this as your quick guide: thin fillets (¼”–⅜”) — 375°F for 12 minutes or 400°F for 10 minutes. Medium fillets (⅜”–½”) — 375°F for 14–18 minutes. Sear+finish — sear 1–2 minutes, then 375°F for 8–10 minutes. In all cases, verify 145°F (63°C) internal temperature.

• Thin (¼”–⅜”): 375°F / 12 min or 400°F / 10 min
• Medium (⅜”–½”): 375°F / 14–18 min
• Sear+finish: sear 1–2 min, then 375°F / 8–10 min
• Target internal temp: 145°F (63°C)

Troubleshooting

If the filling is soggy, the fix is to squeeze the spinach harder and add a bit more panko or a teaspoon of cream cheese to absorb moisture; if it’s dry, stir in ½ tsp olive oil or a splash of lemon juice. Overcooked flounder is dry and flaky — check the internal temp early and pull at 140°F (60°C), letting carryover heat reach 145°F (63°C).

If rolls unroll, set seam-side down and use toothpicks or a dab of cream cheese at the seam as glue. If you’re baking from frozen, add 8–12 minutes to the bake time and always confirm with your thermometer.

Variations & substitutions

For gluten-free, swap panko for gluten-free breadcrumbs or almond meal; for dairy-free, use a firm vegan feta or mash firm tofu with lemon and a pinch of salt. Add crab or shrimp to the spinach mix for a richer stuffing, or fold in sun-dried tomatoes and olives for a Mediterranean twist.

We sometimes swap feta for ricotta + Parmesan when we want a creamier filling; for a brighter sauce, serve with a quick garlic-butter sauce or a squeeze of lemon right before serving. For other recipe ideas featuring feta, see feta chicken thighs with artichoke hearts.

Make-ahead, freezing & storage

You can assemble stuffed fillets and refrigerate for up to 24 hours before baking; wrap tightly to prevent odors. For freezing, wrap raw assembled fillets tightly and freeze up to 1 month — bake from frozen, adding 8–12 minutes to the bake time and confirming 145°F (63°C) before serving.

Store leftovers in an airtight container for up to 3 days and reheat gently in a 325°F (165°C) oven just until warm — this prevents the fish from drying out. Reheating in a skillet over medium-low with a splash of water and a lid for a minute or two also works well.

Serving suggestions and pairings

Serve with roasted asparagus, lemon rice, or herbed new potatoes and a simple lemon-butter or tomato-caper sauce. A crisp Sauvignon Blanc or an unoaked Chardonnay pairs nicely with the briny feta and lemon notes.

For sauce ideas, check our pan sauce guide or try a quick lemon-butter — we link to related recipes like our garlic-butter sauce and other fish-friendly sides for easy pairing suggestions. For selecting and prepping fish, see our guide on choosing fresh fillets like cod or flounder at how to choose and prepare fresh fish.

Printable recipe card

Servings: 4 | Prep: 15 min active, 10 min passive | Cook: 12–18 min (depending on thickness). Target internal temp: 145°F (63°C). Active time mainly prepping and sautéing spinach; passive time is short chill and baking.

1. Preheat oven to 375°F (190°C). Pat 4 flounder fillets dry and prepare pockets or trim for rolling.
2. Sauté 1–2 cloves minced garlic in 1 tbsp oil, add 6 oz fresh spinach and cook 1–2 minutes until wilted; squeeze very dry.
3. Mix squeezed spinach with ¾–1 cup feta, 2–3 tbsp panko (or 2 tbsp cream cheese), 1 tsp lemon zest, 1 tbsp lemon juice, salt and pepper.
4. Fill each fillet with 2–3 tbsp filling, roll or fold, secure with toothpicks, chill 10 minutes if possible.
5. Bake at 375°F (190°C) for 12–18 minutes (thin 10–12 at 400°F), or sear seam-side down 1–2 minutes then finish in 375°F oven 8–10 minutes. Remove when internal temp is 145°F (63°C).
6. Rest 3–5 minutes, remove toothpicks, garnish, and serve.

Process photo: stuffing assembly and a cross-section of a cooked roll make a great reference — include a photo of the filling going into a fillet and a finished cross-section to show doneness and texture (we always shoot the cross-section to show a moist, flaky center).

Related reading

For more on choosing fish and simple sauces, see our posts on selecting fresh fillets and quick pan sauces; we also have a feta-forward chicken idea in feta chicken thighs with artichoke hearts and a handy sauce at garlic-butter sauce. If you want tips on cooking other white fish, check resources like how to choose and prepare fresh fish.

Frequently Asked Questions