Place packs on grill over medium heat. Cover grill; cook 10 minutes. Rotate packs 1/2 turn; cook 9 to 10 minutes longer or until juice of chicken is clear when center of thickest part is cut (at least 165°F). Remove packs from grill; cut large X across top of each pack. Carefully fold back foil; sprinkle potatoes with cheese. Top each chicken breast with 1 tablespoon barbecue sauce, and garnish with green onions.