In a nonstick frying pan, cook the ground beef, pepper and onion until the meat is browned and the vegetables are tender, 7 to 10 minutes. Drain well and return the mixture to the frying pan. Add the tomato soup to the ground beef mixture and stir well. Simmer for at least 10 minutes.
To serve, place 2/3 cup of the meat mixture on each bun. Serve immediately.