Preheat the oven to 200°C.
Salt the hollowed-out tomato cavities and drain upside down on kitchen paper for 15 minutes.
Fry the onion in 60ml of olive oil until softened, then add reserved tomato pulp and half the basil.
Cook the tomato mixture over medium heat for 20 minutes until thickened.
Heat 30ml of oil in a frying pan and dredge aubergine slices in flour.
Dip aubergines in beaten egg and fry until golden-brown, then drain on kitchen paper.
Layer one aubergine slice, a spoonful of sauce, a basil leaf, and mozzarella into each tomato cavity.
Repeat layers until full, replace tomato lids, and place in an ovenproof dish with oil and seasoning.
Bake for 25 minutes until the tomatoes soften and cheese melts.
Garnish with remaining basil and olive oil to serve.