Use top round roast, seasoned with meat tenderizer. Pound the seasoning on both sides of the beef so it is absorbed. Place in crockpot and cook for about 8 hours. Remove the beef and cut into small pieces. Take two slices of bread of toast in the toaster. Place the roast beef on top of the toast. Cut the sandwich in half. Place the two pieces of sandwich on a plate and in the middle of the plate place mashed potatoes. Use the remaining drippings from the crockpot to make gravy. Pour the gravy over the whole plate, including the sandwich and mashed potatoes.