Prep: 20 minutes; Cook: 16 minutes
Combine sirloin, breadcrumbs, 1/4 cup sauce, and salt in a bowl; shape mixture into 12 (1-inch) meatballs.
Heat a large nonstick skillet coated with cooking spray over medium-high heat. Add meatballs; cook 6 minutes, browning on all sides. Drain well. Wipe pan with a paper towel.
Return meatballs to the pan over medium-high heat. Add green bell pepper and onion; cook 3 minutes, stirring occasionally.
Add 1 1/2 cups sauce; cover, reduce heat, and simmer 8 minutes or until thoroughly heated. Spoon meatball mixture into rolls; top with mozzarella cheese and, if desired, basil. Let stand 1 minute before serving to melt cheese.
Note: Nutritional analysis includes Sugars 5g.