Preheat oven (electric cooker: 225 °C/circulating air: 200 °C/gas: see manufacturer). Coat a sheet with oil. Clean, wash and slice the aubergines. Place on a baking tray and bake for about 30 minutes.
Peel and chop onion and garlic. Wash and chop the oregano. Fry onion and garlic in 2 tbsp. hot oil. Sweat tomato paste with. Add strained tomatoes and oregano, bring to the boil. Season with salt, pepper and 1 tsp. sugar and boil down for about 10 minutes.
Wash the tomatoes and cut them into slices. After about 20 minutes baking time, cover aubergines with sauce, tomatoes and mozzarella, bake until done.