1.In a medium bowl, combine beef, egg and breadcrumbs; roll rounded tablespoons of mixture into balls, flatten slightly.
2.In a heated, oiled large frying pan, cook meatballs over medium heat for about 5 minutes, or until browned. Add sauce; bring to the boil. Reduce heat; simmer, uncovered, for about 5 minutes or until meatballs are cooked through. Season to taste.
3.Cut bread in half horizontally, without cutting all the way through. Fill with meatballs and sauce; sprinkle with cheese. Cut into four before serving.