Set the grill to high then cook the aubergine slices until browned on each side. Remove from the grill.
Preheat the oven to Gas 4, 180°C, fan 160°C. Heat the oil in a pan over the heat then add the onions, stirring occasionally until softened. Add the carrots, peppers and courgettes and cook for 15 minutes, stirring frequently.
Mix in the oregano and tomatoes, and simmer for 10 minutes.
Pour some of the veg sauce into an ovenproof dish, top with aubergine slices then add more sauce. Repeat until the final layer is sauce, then top with Parmigiano cheese and mozzarella.
Cook in the oven for 30-40 minutes until golden. Serve with a green salad.
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