Preheat the oven (electric cooker: 225 °C/ circulating air: 200 °C/ gas. level 4) Wash, clean and halve the tomatoes. Peel onion and cut into large cubes. Heat the oil in a casserole dish or ovenproof pan suitable for the stove. Add tomatoes and onion and fry for 8-10 minutes.
Season with 1/2 teaspoon of seasoning. In the meantime, whisk eggs, milk, rest of tomato and mozzarella seasoning and pepper. Coarsely grate the feta cheese and stir it into the egg milk until 1/3. Cut the mozzarella into slices. Wash the rosemary, dab dry and remove the needles. Add the rosemary 2 minutes before the end of the cooking time and fry. Add olives and pour egg milk over it. Sprinkle with the remaining feta cheese and spread mozzarella on top. Leave in the oven for about 15 minutes.
Wash the rosemary, dab dry and remove the needles. Add the rosemary 2 minutes before the end of the cooking time and fry. Add olives and pour egg milk over it. Sprinkle with the remaining feta cheese and spread mozzarella on top. Leave in the oven for about 15 minutes. Serve garnished with basil