In large shallow dish or resealable food-storage plastic bag, mix marinade mix, water and oil. Add pork chops and onion; turn to coat. Cover dish or seal bag; refrigerate 30 minutes to marinate.
Heat gas or charcoal grill.
When grill is heated, remove pork and onion from marinade; reserve marinade. Place pork and onion on gas grill over medium heat or on charcoal grill over medium coals; cover grill. Cook 10 to 15 minutes, turning once and brushing frequently with marinade, until pork is no longer pink in center. Discard any remaining marinade.