Preheat oven (electric cooker: 225 °C/circulating air: 200 °C/ gas: level 4). Wash and halve the tomatoes. Peel and roughly dice onion. Steam both in hot oil in a pan for about 10 minutes. Turn carefully in between. Season with half the tomato and mozzarella seasoning
Whisk the eggs, milk, the rest of the tomato and mozzarella seasoning and pepper. Coarsely grate or crumble the feta cheese and stir it into the egg milk until 1/3 of it is dissolved
Cut the mozzarella into slices. Wash and pluck the rosemary. Add to the tomatoes and fry briefly
Fill tomatoes and olives into a wide fireproof dish. Pour egg milk over it. Sprinkle with the remaining feta cheese. Spread mozzarella on top. Leave to set in a hot oven for about 15 minutes. Garnish with basil. Served with: white bread