Cut the aubergines lengthways into about 1 cm thick slices, add them to the hot pan in portions and fry for 3-4 minutes on each side. Drain the fried aubergine slices well on kitchen paper.
Put the tomatoes in a bowl and chop them up, season with garlic, salt, pepper, oregano and other spices of your choice.
Put a layer of aubergines in a baking dish, cover with a layer of the tomato sauce and top with a few slices of mozzarella. Continue like this until the eggplant and cheese are used up. Finish with a layer of tomato sauce.
Sprinkle the gratin with the parmesan and bake in the preheated oven for 30 minutes at 200 ° C.
The gratin can not only be served hot, for example with rice, but also tastes very good cold, for example with white bread.