I use to make this for my family and it was always a big hit with them.
Cut thin slice from the top of each roll; scoop out. Crumble enough of the insides to make 1-¼ cups; reserve. Cover the rolls to prevent drying.
Combine beef, egg, salt, pepper, milk and the reserved crumbs in medium bowl; mix well. Shape into 1-inch balls (about 27).
Brown part of meatballs at a time in oil in large skillet. Remove to large bowl. Add more oil to skillet and sauta© peppers and onion until tender. Remove to bowl.
Stir flour into fat remaining in skillet and heat through until bubbly. Stir in chili sauce and water.
Cook stirring constantly until sauce thickens and bubbles. Stir in brown sugar and mustard. Add meatballs and pepper mixture; cover and simmer 20 minutes.
Heat rolls in slow oven 325 degrees for 10 minutes. Spoon meatballs and sauce into hero rolls.