Spray the frying pan with low-calorie cooking spray and place over a medium heat. Add the onions, grated apple, and a pinch of salt. Fry for 5 minutes until softened. Allow to cool.
Place the pork mince in a bowl and add the apple, onions, and Branston pickle. Season with some salt and pepper, then mix until thoroughly combined.
Divide into 4 even portions, then shape into burgers approximately 12cm in diameter (we used a burger press, but you can shape by hand if you want).
Spray the air fryer basket with low-calorie cooking spray, then air-fry the burgers at 200°C for 6-8 minutes — flipping halfway through. You'll know that the burgers are cooked when they're firm to touch and the juices run clear.
Turn off the air fryer, then pop a cheese slice on top of each burger, and close the drawer. Leave for a minute or two. The residual heat from the air fryer will be enough to melt the cheese.
Split the rolls, and fill with the leaves, tomatoes, and onions. Put a burger on top and add a teaspoon of pickle to the top. Then close the bun and tuck in!