Preheat the oven to 160°C. Spray a large frying pan with low-calorie cooking spray and set on a medium heat. Add the meatballs and fry for 4 minutes until browned on all sides.
Add the garlic and chillies and cook for 2 minutes, being careful not to burn it. Stir in the passata and oregano.
Pour the sauce and meatballs into a large ovenproof dish.
Top with chunks of the mozzarella and sprinkle over the Parmesan. Bake for 35 minutes until the cheese is golden brown and bubbling, and the meatballs are cooked through. Serve with your choice of accompaniment.