HEAT grill to medium-high heat.
RESERVE 2 Tbsp. dressing. Spray both sides of chicken with cooking spray. Grill 10 min. or until chicken is done (165ºF), turning and brushing occasionally with the reserved dressing. Remove from grill. Let stand 5 min.
CHOP chicken; place in large bowl. Add lettuce, tomatoes, pasta, shredded cheese and onions; mix lightly. Add remaining dressing; toss to coat.
SPRINKLE with Parmesan.