HEAT oven to 450ºF.

PLACE fish on baking sheet sprayed with cooking spray. Brush with 2 Tbsp. dressing. Bake 12 to 15 min. or until fish flakes easily with fork.

MEANWHILE, heat oil in large nonstick skillet on medium heat. Add next 3 ingredients; cook and stir 4 min. or until crisp-tender. Remove from heat; stir in remaining dressing.

SPOON cooked vegetables onto serving plate; top with fish and onions.