Clean, wash and dry the zucchini and cut them diagonally into thick slices. Remove the crusts from white bread and chop finely in a universal chopper. Heat 2 tablespoons of oil in a pan and toast the white bread crumbs in it. Finely grate the Parmesan cheese. Finely chop the basil and rosemary. Finally add to the white bread and mix with another tablespoon of oil. Spread the zucchini slices with oil and spread the white bread mixture on top.
Bake in a preheated oven (electric cooker: 200 °C/ gas: level 3) for 12-15 minutes. In the meantime, clean, wash and slice the tomatoes. Peel onion and cut into rings. Mix remaining oil and vinegar and season with salt and pepper. Arrange tomatoes and onions on a plate and pour the vinaigrette over them. Arrange the zucchini au gratin and serve garnished with olives, basil, rosemary and parmesan slices.