place 8 lemon slices on grill grate; top with fish. brush with some of the remaining dressing mixture. grill 5 min.; turn.
add remaining lemon slices and asparagus to grill. cook 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 grill. discard lemon slices under fish. serve remaining lemon slices with fish and asparagus. 