Heat the oil in a frying pan, add the onion and cook until it's very soft and lightly caramelised.
Add the garlic and cook for another couple of minutes.
Take the pan off the heat, tip the onion and garlic into a bowl and leave them to cool.
Add the remaining burger ingredients to the cooled onion and garlic.
Season well with salt and pepper, then put the mixture in the fridge to chill for a couple of hours.
Shape the mixture into 8 patties weighing about 100g each. You can then put them in the fridge again until your are ready to cook. At this stage, you can open freeze them, then transfer to a freeze-proof container when frozen.
When you are ready to cook the burgers, preheat the oven to 200 degrees C (180 in a fan oven).
Spray a baking tray with low-cal oil, arrange the burgers on the baking tray, and spray them with low-cal oil.
Bake for 20 minutes.
Lightly toast the burger buns, then layer up the burgers with the salad ingredients and condiments of your choice!
Serving Size Makes 8 burgers