Preheat the air fryer to 200C (see Don't have an air fryer?). Whisk 1 egg in a bowl. Put 3 tsp pepper and garlic seasoning (see Cooking tip) in a shallow bowl. Put the breadcrumbs in a separate shallow bowl. Pat the fish dry with paper towel. Dust the fish with the seasoning, shake off the excess, then dip in the egg and coat in the breadcrumbs.
Step 2 — Air-fry fish
Generously spray both sides of the crumbed fish with olive oil and put in the air-fryer basket, in batches if necessary. Air-fry the fish, turning halfway, for 15 mins or until golden and cooked through.
Step 3 — Make tartare sauce
Meanwhile, finely chop the capers. Combine the capers and 2 tbs mayonnaise in a bowl and season with salt and pepper. Combine 1 tbs olive oil and 2 tsp red wine vinegar in a large bowl and season with salt and pepper. Add the salad leaves and toss to coat.
Step 4 — Toast buns
Cut the buns in half, then sandwich the halves back together again. Put the buns in the air-fryer basket. Air-fry for 1-2 mins until lightly toasted.
Step 5 — Serve up
Spread the bun bases and tops with the tartare sauce and layer with the fish and some salad leaves. Divide the burgers and remaining salad leaves among plates. Enjoy!
Step 6 — Don't have an air fryer?
No worries, you can cook the fish in a frypan and grill the buns in the oven. Heat 2 tbs olive oil in a medium frypan over medium-high heat and cook the fish for 3-4 mins each side until golden and cooked through. To toast the buns, preheat the grill to high. Put on an oven tray, cut-side up, and grill for 2-3 mins until lightly toasted.