Peel the onions and cut into fine wedges. Pat the schnitzel dry. Heat the oil in an ovenproof pan (with a lid). Fry the schnitzel vigorously on each side for 1-2 minutes. Season with 1 teaspoon pizza spice, pepper and a little salt. Spread the onion wedges over the top. Remove the pan from the stove.
Place 1 slice of ham on each schnitzel. Quarter the meat, shape it into an oblong shape and place on top.
Season the chunky tomatoes with salt, pepper and pizza seasoning. Mix with the cream and pour over the schnitzel. Cover and simmer in a preheated oven (electric stove: 175 ° C / fan: 150 ° C / gas: level 2) for about 1 1/4 hours.
Dice the mozzarella. Sprinkle the schnitzel with mozzarella and Gouda cheese. Bake open for another 20-25 minutes.