Heat a large nonstick skillet over medium heat. Add oil; swirl to coat. Add onion; cook 3 minutes.
Add beef; cook 4 minutes or until beef begins to brown, stirring to crumble.
Stir in tomato sauce and next 7 ingredients (though tomato paste); bring to a simmer. Cook 5 minutes or until slightly thickened, stirring occasionally.
Divide beef mixture evenly among bottom halves of buns; top with top halves of buns.