Pat the fish fillets dry with paper towels and season both sides with 1/2 tsp salt, 1/4 tsp pepper, 1/2 tsp smoked paprika and 1/2 tsp dried oregano. Drying the fish removes surface moisture so it crisps rather than steams in the air fryer; the spices add aroma and a savory crust without heavy batter.

Thinly slice the potato into 2–3 mm rounds (a mandoline is ideal) and place in a bowl of cold water for 5 minutes, then drain and dry thoroughly. Soaking and rinsing removes excess surface starch so the rounds crisp and brown more evenly in the air fryer.

Core and cut the tomatoes into thick wedges (about 6 wedges total) and slice the onion into 6–8 wedges. Toss the tomatoes and onions gently with 1 tbsp olive oil, 1/4 tsp salt, 1/4 tsp pepper, the minced garlic and 1/2 tsp oregano. Coating the vegetables in oil helps them caramelize and protects delicate tomato flesh in the hot air stream.

Preheat the air fryer to 200°C (400°F) for 3–5 minutes. A hot start ensures immediate browning on contact; air fryers need a moment to reach steady airflow and temperature for consistent results.

Toss the dried potato rounds with 1/2 tbsp olive oil and a pinch of salt. Arrange them in a single layer in the air fryer basket (work in a single layer or two quick batches to avoid overcrowding). Air-fry at 200°C (400°F) for 8–10 minutes, flipping halfway, until edges are golden and crisp. Keeping the rounds single-layered exposes each side to hot circulating air so they turn crisp rather than soggy.

While the potatoes cook, air-fry the tomato and onion wedges in a single layer at 200°C (400°F) for 8–10 minutes. Shake or turn once at 4–5 minutes so they brown evenly. The goal is soft, lightly blistered tomato with sweet, slightly charred edges on the onion — chilling and separation of cook times prevents overcooking.

After the vegetables are done, give the air fryer 1 minute to cool slightly. Brush the fish fillets with the remaining 1/2 tbsp olive oil and a light squeeze of lemon juice. Place fish skin-side down (if skin-on) in the basket, leaving space between fillets. Air-fry at 200°C (400°F) for 8–10 minutes (depending on thickness) until the exterior is lightly golden and the fish flakes easily with a fork. High, dry heat is used to produce a lightly seared exterior while keeping the interior moist; cooking time varies with thickness—aim for an internal temperature of 60°C / 140°F for flaky, opaque fish.

While the fish rests for 2 minutes (this lets juices redistribute), melt the butter in a small pan or microwave with the remaining lemon zest and a pinch of salt. Spoon the lemon-butter over the fish just before serving and sprinkle chopped parsley on everything. Resting also allows the residual heat to finish gentle cooking without drying the fillet.

To plate: fan the potato rounds on one side, place a fillet atop or beside them, and spoon the blistered tomato and onion wedges around. Finish with a drizzle of lemon-butter, a scatter of parsley and a small pinch of chili flakes if using. The contrast of textures — crisp potato, silky fish, and sweet-sour roasted vegetables — is the centerpiece of the dish.