Cut the baps in two
Thinly slice the tomato and onion
In a frying pan, gently fry the sliced onion with the olive oil over a gentle heat
Add the beef burgers and season with salt and black pepper
Once cooked, place the beef burger onto the bap which you have already spread with a mixture of ketchup and mustard
Add the lettuce, sliced tomato and onion
Place the other half of the bap on top
Tip : To enjoy even more crunch, toast the baps before adding the burgers.