Sour and salt the fish fillets. Then turn in flour and cut into pieces. Then fry in oil and place in a buttered casserole dish.
Fry the onions, tomatoes and mushrooms in the frying fat, season and place on the fish. Sprinkle cheese on top and bake in a preheated oven at 200 ° C for about 20 minutes.
Boiled potatoes or mashed potatoes and salad go well with this.