##brush mushrooms## and if necessary wake and halve them. Onions peel and chop. Heat 1-2 tablespoons of oil in a pot. Fry the mushrooms for about 5 minutes, turning them until golden brown. Season with salt and pepper.
Sauté half ##onions## in the cooking fat. Add rice and fry briefly. Add wine and stock, bring to the boil and simmer covered for about 20 minutes.
In the meantime, cut the cheese into 8 cubes for the meatballs. #Finely dice the tomatoes. Knead minced meat, remaining onions, tomatoes, egg, breadcrumbs and mustard. Season with salt and pepper. Form 8 meatballs from the minced meat mixture, filling each with a cheese cube.
Heat 2 tablespoons of oil in a large frying pan. Fry the meatballs for 5-6 minutes on each side.
Wash oregano and shake dry, chop. Stir butter, mushrooms and oregano into the rice and heat up briefly. Season to taste with salt and pepper. Serve everything.