When meat is frosty, but not frozen, slice into very thin pieces using a sharp knife. If desired, soak overnight in salt water or milk.
Salt and pepper meat. Dredge in flour. Brown in small amount of oil in skillet using medium heat. After meat is browned, add ½ c. of water, cover meat with onion rings, cover and simmer over low heat until meat is tender.
Slice bread length-wise. Spread butter or margarine on each side and sprinkle with garlic powder. Lay slices of meat on bottom half of bread, top with onions if desired, spread cheese over top of meat and onions, top with other half of bread. Wrap in foil, heat in 300F oven until bread is crusty. Cut into serving-size pieces and serve with sliced pickles, peppers, tomatoes, etc.