1. Cook pasta according to package directions, omitting salt.
2. Meanwhile, heat oil in medium skillet over medium-high heat. Sprinkle chicken with garlic salt and pepper; cook chicken 5 to 7 minutes or until browned, turning once. Remove from skillet; set aside. Add onion to skillet; cook 1 to 2 minutes over medium heat or until crisp-tender.
3. Add undrained tomatoes and vinegar to skillet; bring to a simmer. Return chicken to skillet; cook 10 to 12 minutes more or until chicken is no longer pink in centers (165°F).
4. Serve chicken and sauce with pasta. If desired, slice each chicken breast before placing on pasta.