Peel all onions. Halve red onions, cut vegetable onions into approx. 1 cm thick slices. Steam in hot oil while turning for about 10 minutes at medium heat. Season with salt and pepper.
In the meantime clean, wash and halve the tomatoes. Wash parsley, chop roughly. Mix eggs, milk and parsley. Season with salt and pepper. Pizza dough en
Spread onions and tomatoes on top. Pour the egg milk over them. Cut the cheese into slices and cover with it. Bake in the preheated oven (electric oven: 200 °C/ gas: level 3) for 25 - 30 minutes.
Cover up in between if necessary. Serve garnished with parsley.