Start by removing your flounder fillets from the refrigerator about 5 minutes before cooking—this takes the chill off slightly, which helps them cook more evenly. Pat them completely dry with paper towels. This step is crucial. Any surface moisture will steam rather than allow the exterior to develop that subtle golden tone we're after. I use firm pressure and make sure I've dried the underside too, which many home cooks miss. If your fillets are particularly thin (which flounder often is), handle them gently. These are delicate proteins and rough handling can tear the flesh. Lay them on your prep surface and they should feel tender but intact.

Here's where the decision about capers matters: if you're using them, skip the salt entirely. Capers are packed in brine and contribute significant saltiness—I learned this the hard way years ago when I over-salted a beautiful sea bream and couldn't salvage the dish. If you're not using capers, season both fillets with ¼ teaspoon salt divided between them (a pinch on each side). Next, sprinkle the garlic powder, oregano, and paprika evenly across both fillets. I use my fingertips to gently distribute the seasoning, ensuring it contacts as much surface area as possible. The garlic powder brings savory depth without the harshness of fresh garlic, which can overwhelm delicate fish. The oregano is a nod to Mediterranean coastal cooking, where flounder has been prepared for centuries, and the paprika adds both color and a subtle sweet smokiness. Finish with a couple pinches of freshly ground black pepper on each fillet. Black pepper is one of those ingredients where freshness genuinely matters—pre-ground pepper loses volatile oils over time and tastes dusty. Always crack yours fresh if possible.

Preheat your air fryer to 375°F for about 3 minutes while you finish prep. This temperature is the sweet spot for flounder—hot enough to cook the fish through and create a subtle exterior, but not so hot that the thin fillets dry out before they cook through. Once preheated, give your basket a light coating of oil spray. I use about 2-3 quick sprays, just enough to create a thin layer. The goal isn't a pool of oil; it's preventing the fish from sticking while keeping the recipe light. Avocado oil spray is my choice because it has a high smoke point and neutral flavor, but any cooking oil spray works.

Now arrange your lemon slices in a single layer across the basket. You'll want them fairly close together—they should cover most of the oiled surface. These lemon slices serve multiple purposes: they prevent the fish from sticking directly to the basket, they infuse the fillets with subtle citrus as they cook, and they create a steaming microclimate that keeps the delicate fish incredibly moist. I typically use 4-6 thin lemon slices, depending on the size of my air fryer basket. If your slices are thick, they might not soften in time. Aim for slices about ¼-inch thick—thin enough that they'll become tender, but thick enough that they don't fall apart.

Carefully place your seasoned flounder fillets on top of the lemon slices. Position them so they're in a single layer and not overlapping—air circulation is what makes air fryers work, and overcrowding prevents that circulation. If your fillets are very large, you might need to cut them in half, which is perfectly fine. The fish should be nestled gently on the lemon bed. You're not pressing it down; just laying it to rest on the citrus cushion.

If you're using capers, distribute them across the top of the fillets now—about ½ tablespoon per fillet. The capers will warm through and their brininess will distribute throughout the fish. If you're using butter, dot a small amount (½ teaspoon per fillet) across the top. The butter will melt and create a light, golden finish while adding richness that plays beautifully against the lemon. If you're not using either, that's absolutely fine. The fish will still be delicious—just skip this step and move forward.

Place the basket in your preheated air fryer and set the timer for 7 minutes. This is the key timing for standard flounder fillets (about 5-6 ounces each). If your fillets are thicker than typical or you're cooking for more people with a larger piece, you might need 8-9 minutes, but start with 7 and check. Don't open the air fryer during cooking. Trust the process. The circulating heat is working, and opening the basket drops the temperature and interferes with cooking.

When the timer sounds, carefully open your air fryer. The flounder should be opaque throughout, with flesh that flakes easily when prodded with a fork. The edges might have a hint of golden color, and the lemon slices beneath should be soft and slightly caramelized. The internal temperature should read 145°F on an instant-read thermometer at the thickest part of the fillet—this is the USDA safe minimum for fish. If it's not quite done, give it 1-2 more minutes and check again. Fish cooks quickly, so these small increments matter.

Remove the basket from the air fryer and let the flounder rest for 1-2 minutes. This brief rest allows the residual heat to finish cooking the center while the exterior sets. Carefully transfer the fillets to a serving plate, and if you'd like, arrange a lemon slice or two from the basket alongside the fish for presentation and extra flavor. Serve immediately while everything is warm and the butter (if used) is still glossy.