Clean, wash and slice the zucchini. Clean, wash and slice the mushrooms. Quarter peppers, remove seeds, wash and cut into strips. Peel, wash and slice potatoes.
Clean, wash and halve the tomatoes. Heat the oil in a pan in portions and first fry the potato slices in it until golden brown. Season with salt. Fry the rest of the vegetables in the frying fat. Season with salt and pepper.
Take it out. Grease 2 ovenproof dishes and line each with half of the fried potatoes. Spread half of the vegetables and half of the tomatoes on each. Wash oregano and dab dry. Pluck the leaves from the stalks, except some for decoration, and chop them coarsely.
Sprinkle oregano over the vegetables. Grate cheese and sprinkle on potato pizzas. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 25 minutes until golden brown. Garnish with oregano and serve immediately.