Boil the potatoes in salted water, peel and allow to evaporate, then cut into cubes. Finely dice 1 zucchini, tomatoes and hard egg.
Make a dressing from vinegar, oil, a little mustard, salt and pepper and mix everything with it.
Cut the remaining 2 zucchini into thick slices and bread them with the raw egg and breadcrumbs like schnitzel. Fry in plenty of vegetable oil until crispy brown.