Mix the red onion with the minced beef and season with salt and pepper.
Shape the beef into a burger patty and insert the mozzarella into the centre.
Heat olive oil in a non-stick frying pan and cook the burger for 5 minutes per side.
Remove the burger from the heat and let it rest for 3 minutes.
Dip the courgette matchsticks into the 100ml of milk and then coat them in flour.
Heat the vegetable oil in a saucepan until a breadcrumb sizzles gently.
Deep fry the courgettes for 4 minutes until they are golden brown.
Remove the fries with a slotted spoon and drain on kitchen towels before serving with the burger.