Roughly dice the onion and sauté in the oil. Add the ground beef and season well with mustard, ketchup, salt, pepper, paprika and oregano. Fold in the pitted and finely chopped peppers. Let everything stew for 8 minutes while stirring.
Cut the tomatoes into slices and coarsely grate the cheese.
Thoroughly grease a baking dish.
Cover the bottom of the pan with potato slices.
Mix the minced meat with some tomato slices and spread over the potatoes, sprinkle with 3 tablespoons of cheese. Place the remaining potatoes in a tile-like manner, alternating with the tomato slices, and sprinkle with the remaining cheese.
Bake on the top rack for about 30 minutes until the cheese begins to brown.