Heat oven to 220C/200C fan/gas 7. Brush both sides of the aubergine slices with oil, then lay on a large baking sheet. Bake for 15-20 mins until tender, turning once.
Meanwhile, put the spinach in a large colander and pour over a kettle of boiling water to wilt. Cool, then squeeze out the excess water, so that it is dry. Mix with the ricotta, nutmeg and plenty of seasoning.
Dollop a spoonful of the cheesy spinach mix in the centre of each aubergine slice, fold over to make a parcel and lay, sealed-side down, in an ovenproof dish. Pour over tomato sauce, sprinkle with breadcrumbs and cheese, and bake for 20-25 mins until golden and piping hot.