1. Place a frying pan over heat and add the olive oil and onion. Cook for 5 minutes or until it begins to golden.
2. In a bowl, add the mince, herbs and beaten egg. Season with salt and pepper and add the onions. Mix well, then use your hands to shape into 4 even patties.
3. Cook the burgers on a preheated pan or barbecue for 5-6 minutes on one side. Flip the burger and while the second side is cooking, place a slice of cheese on top of the meat to slightly melt (optional).
4. Lightly toast the inside of the buns then add lettuce, burgers and tomato slices, alongside any sauces you would like.