Mix the ketchup, Italian dressing, soy sauce, and molasses in a small bowl. Place the steak in slow cooker, sprinkle with onions, and pour the ketchup mixture over the steak.
Turn the slow cooker to High and cook for 1 hour. Reduce the heat to Low and continue cooking until the meat is tender, about 4 hours. Serve on hoagie buns and top with 1/4 cup coleslaw, if desired, for a Southern BBQ flavor.