Meanwhile, chop sweet onion and bell peppers. Chop the green onion, setting green section aside separately. Mince garlic. Heat a large nonstick skillet over medium. Add onions (except the green section), peppers, and garlic to skillet; cover and cook for 2-3 minutes. Stir then cover and cook 2-3 minutes longer.
Add beef, salt and basil to skillet. Cook until no longer pink, stirring to crumble.
Add marinara and cook until heated through. Stir in cooked pasta and mozzarella. Turn off heat and add greens of onion.