Peel onions and cut them into rings. Line a greased grease pan of the oven with it. Clean, wash and drain the leek and tomatoes. Cut leek into rings, tomatoes into slices.
Drain mushrooms well. Wash parsley, shake dry, pluck off leaves and chop.
Dab schnitzel dry, season with salt and pepper. Spread the schnitzel on the onions, spread minced pork on the schnitzel. Cover with leek, tomatoes, about half of the parsley and mushrooms.
Bake in the preheated oven (electric cooker: 250 °C/ convection oven: 225 °C/ gas: see manufacturer) on the lower rack for approx. 50 minutes. Mix the cream with the sauce powders. About 15 minutes before the end of the cooking time, pour over the escalopes and cover with cheese.
Finally, bake, arrange and sprinkle with the remaining parsley.