MIX dressing and lemon juice; pour half into large resealable plastic bag. Add fish; seal bag. Turn bag over several times to evenly coat fish. Refrigerate 15 min. to marinate. Refrigerate remaining dressing mixture for later use.

MEANWHILE, heat barbecue to medium heat. Cut each lemon into 4 slices; place 8 slices on barbecue grate. Remove fish from marinade; discard bag and marinade. Place fish over lemon slices on barbecue; brush with some of the reserved dressing mixture. Cover barbecue with lid.

GRILL fish 5 min.; turn over. Add remaining lemon slices and asparagus to barbecue. Grill 5 min. or until fish flakes easily with fork and asparagus is crisp-tender, brushing occasionally with remaining dressing mixture. Remove fish, lemon slices and asparagus from barbecue. Discard lemon slices under fish. Serve remaining lemon slices with the fish and asparagus.