Wash the aubergines and cut them into 1 centimeter thick round slices. Heat 5 table spoons olive oil in a big nonstick pan and fry the aubergines until almost tender, about 3 minutes for each side. Spread the rest of the oil on a cookie sheet. Arrange the aubergine slices on the cookie sheet and sprinkle them with salt and pepper. Cut the tomatoes into thin slices and put one tomato slice on every aubergine. Grate the cheese and spread it evenly over the aubergines. Sprinkle oregano over it and bake it in the oven under the grill, until the cheese has formed a lovely, golden crust on top of each aubergine slice and the aroma of oregano has spread in your kitchen.
If you want to prepare this dish in advance, fry the aubergines and top them with the rest of the ingredients. Cover everything with aluminum foil and keep it in the fridge until you need it. When you finally are ready to finish, bake your aubergines first for 5 minutes at 200 degrees in the oven before you switch to the grill to gratin the cheese. In this way you are sure that the aubergines will be warm when you finally serve this dish.