Remove and discard giblets and neck from chicken. Rinse chicken under cold water; pat dry. Trim excess fat from chicken.
Place onion in cavity of chicken. Brush chicken on all sides with about one-third of teriyaki sauce. Sprinkle with garlic pepper seasoning. Lift wing tips up and over back; tuck under chicken. Place chicken, breast side up, on a broiler pan coated with cooking spray. Insert meat thermometer into meaty part of thigh, making sure not to touch the bone. Pour remaining teriyaki sauce over chicken.
Bake, uncovered, at 375° for 1 1/2 hours or until thermometer registers 180°. Remove and discard skin before eating, if desired (analysis does not include skin).