Make the tomato sauce. Heat the oil in a saucepan, add the garlic and onion and fry for 3–4 minutes until softened. Add the tomatoes and basil, bring to the boil and simmer for 15 minutes.
Brush the aubergines with the oil on each side while the sauce is simmering. Heat a griddle until hot and cook the aubergine slices for 1–2 minutes on each side until tender and browned.
Spoon a little of the tomato sauce into an ovenproof dish, layer over half the aubergines, scatter over half the mozzarella and Parmesan and season well. Repeat the layering with the remaining ingredients, finishing with a scattering of the cheeses.
Place in a preheated oven, 200°C (400°F), Gas Mark 6, for 20–25 minutes until golden and bubbling. Serve with salad and crusty bread.