Fry the onions in oil, add the tomato sauce and simmer. Season to taste.
Mix the minced meat with egg, breadcrumbs and spices to taste and shape into meatballs. Place the meatballs in the sauce and simmer for about 30 minutes.
Preheat the oven to circulating air 180 degrees. Grease a baking dish, layer in the dumplings and pour the sauce with the meatballs on top. Sprinkle with cheese and bake for about 30 minutes.