HEAT grill to medium heat.
PLACE 1 Tbsp. dressing in shallow plate. Place fish, skin side up, in dressing to coat.
MEANWHILE, mix remaining dressing and all remaining ingredients until well blended; refrigerate until ready to serve.
PLACE fish, skin side down, on grill. Cover grill. Grill 10 min. or until fish flakes easily with fork. Serve topped with sour cream mixture.