Put the meat in an ovenproof dish and brush with the sour cream (if you like it creamier, you can also use crème fraîche). Cut the onion into rings and spread over the schnitzel along with the diced ham. Finally sprinkle everything with a little cheese. Place in the hot oven for about 10 minutes until the cheese has melted.
Baked potatoes go well with it (if the oven is on anyway) or pasta with cream sauce.