Cut the potatoes into slices about half a centimeter thick. Cook in boiling salted water for about 25 minutes. Scald the tomatoes briefly and peel them. Like the onions, cut into thin rings.
Layer the potatoes, tomatoes and onions in a greased baking dish like a roof tile. Salt and pepper each layer and sprinkle with oregano. Drizzle with vegetable stock and oil. Sprinkle the top layer with grated cheese.
Bake at 175 ° C for 15-20 minutes until the cheese crust is golden brown.