Pat the 340 g cod dry and cut it into four equal portions. Season lightly with salt and black pepper.

Put the egg whites and panko in separate shallow bowls. Coat each portion in egg whites, then press into the panko. Use up to 30 g panko for the four portions.

Lightly spray the coated fish with neutral oil. Air-fry in a single layer at 390°F for about 8–12 minutes, working in batches if needed, until the thickest part reaches 145°F (63°C).

Mix the light mayonnaise, plain fat-free Greek yogurt, relish and finely chopped fresh dill. Taste, then add salt, pepper and zero-calorie sweetener only if needed.

Divide the fish, cheese and tartar sauce among four Culture keto buns. Serve while the fish is crisp.