Heat 1 tbsp of the oil in a frying pan over a medium heat and cook the garlic, onion, courgette, carrot, mushrooms and parsley with a little seasoning for 8 mins, stirring regularly, until soft. Set aside to cool completely.
Mix together the fried veg, cheese, egg, breadcrumbs and beef with a little seasoning until well combined. Form into 4-6 burger-sized patties. Can be frozen for up to two months. Defrost thoroughly before cooking.
Heat the remaining vegetable oil in a non-stick frying pan and cook the patties (you may need to do this in batches) for about 3-4 mins on each side until well browned and cooked through.
Build the burgers with the remaining ingredients, and any more you fancy.