Place the ground turkey in a large mixing bowl. Add the mayonnaise, Worcestershire sauce, Dijon mustard, grated onion, garlic, salt, and black pepper.
Mix everything gently with your hands or a fork until the ingredients are just combined. Do not overmix the turkey mixture, as this can make the burgers firm after cooking. The mixture will feel softer than a beef burger mixture, especially because there is no egg or breadcrumbs, but it should still hold together once shaped.
Divide the mixture into 4 equal portions and shape them into burger patties. Make the patties slightly wider than your burger buns because they will shrink a little as they cook. Press a small dent in the centre of each patty with your thumb to help them cook evenly.
Place the patties on a plate or tray and chill them in the fridge for at least 20 minutes if you have time. This step helps the turkey burgers firm up and hold their shape better in the air fryer.
Preheat the air fryer to 383°F / 195°C for 3 minutes. Place the turkey patties in the air fryer basket in a single layer, leaving a little space between each one. If your air fryer basket tends to stick, spray it lightly with oil before adding the patties.
Cook the turkey burgers for 10 to 12 minutes, flipping them carefully halfway through. The exact cooking time depends on the thickness of the patties and your air fryer model. They are ready when the centre reaches 165°F / 74°C on a meat thermometer.
If you want to make air fryer turkey cheeseburgers, add a slice of cheese on top of each patty during the last minute of cooking. Close the air fryer drawer and let the cheese soften.
Let the burgers rest for 2 minutes before serving. Place them in burger buns with lettuce, tomato, pickles, onion, cheese, and your favourite sauce.