Mix all the patty ingredients together in a bowl. It’s best to mix with your hands, as this helps to bring the meat together.
Shape the mixture into 4 oval patties about 1cm thick and leave to rest in the fridge for 15 minutes.
While the patties are resting, spray your frying pan with some low-calorie cooking spray and place over a medium heat. Add the onion to the pan and cook for 5 minutes, until they begin to soften.
Push the onions to the edges of the pan and put your bacon medallions in. Cook them for 2 minutes on each side, or until cooked through to your liking. Transfer the bacon and onions to a plate and cover with foil while you cook the burgers.
Cut your buns in half. Spray with low-calorie cooking spray on the cut side and place in the frying pan to toast for 1-2 minutes. Once done, set aside.
Spray the frying pan with more low-calorie cooking spray and set on a medium heat. Cook the burgers for around 5 minutes each side until cooked through. If using a barbecue, spray the burgers with low-calorie cooking spray before placing on the griddle to cook.
Once the burgers are cooked, turn off the heat and put a slice of cheese on each burger. Place a lid or large plate over the pan and set aside while you prepare the sauce.
Mix all the sauce ingredients together in a small bowl until smooth.
On the bottom half of the bun place a burger, a bacon medallion, some onion and sauce, then add the top half of the bun. Serve with a side of your choice.