Preheat the oven to gas 6, 200˚C, fan 180˚C.
Coat the aubergine and courgette slices in olive oil. Heat a griddle pan and sear the slices for 3-4 minutes each side. Transfer to a plate and repeat until all the slices are griddled.
Add the onion to the griddle pan and cook for 3-4 minutes stirring until it has softened. Meanwhile heat the chopped tomatoes and garlic in a small pan. Add the onion and let it bubble for a few minutes.
Spoon a little tomato sauce into the base of a large ovenproof dish. Then layer with vegetables, sauce and mozzarella. Sprinkle with breadcrumbs and Parmesan, then bake for 35-40 minutes until golden brown on top.