Cut the steaks down the middle, to form a pocket. Fill them with the steamed onions and mushrooms. Optionally, you can fill them with cheese and ham. Put them into a baking dish, put the remaining steamed vegetables in, add the remaining wine and cover the dish with aluminum foil.
You can steam them in a cook pot as well. Bake for about 1 hour, remove the lid at the end to brown them.