Mix Gravy Mix, vinegar and oil in small bowl with wire whisk until well blended. Place chicken in large resealable plastic bag or glass dish. Add marinade; turn to coat well.
Refrigerate 30 minutes or longer for extra flavor. Remove chicken from marinade. Discard any remaining marinade.
Grill chicken on well-oiled grill grates over medium heat 5 to 7 minutes per side or until cooked through. Cool chicken slightly then cut into bite-size chunks.
Mix mayonnaise, orange juice and mustard in large bowl until well blended. Add chicken, celery, cranberries and pecans; mix well. Serve chicken salad on lettuce leaves and tomato slices.