Peel the potatoes and zucchini and grate them into slices. Cut the boiled ham into cubes.
Finely chop the onion and fry it with the ketchup in the pan first. Add the potatoes, zucchini, sour cream and vegetable stock and season well with pepper and oregano. Let cook for 8 minutes. Put the ham in the baking dish, then add the mixture from the pan and sprinkle with the cheese.
Now bake in a preheated oven at 190 ° degrees fan oven for about 20 minutes.