Fry the ham cubes in a non-stick pan, remove and leave to cool on kitchen paper. Heat the butter in the same pan and sauté the onion strips until translucent. Also let cool on kitchen paper, separate from the ham cubes.
Mix the onion strips with the sour cream, tomato paste and wine or broth, season and pour into a baking dish. Knock the medallions flat with the heel of your hand, season with meat seasoning on both sides and place in the baking dish. Mix the ham cubes with toast crumbs and parsley, season with pepper. Spread the mixture on the medallions and press down well.
Bake in a preheated oven at 180 ° C for about 25 minutes.