When ready to grill, spray skin side of salmon with nonstick cooking spray. Place salmon, skin side down, on gas grill over medium heat or on charcoal grill 4 to 6 inches from medium coals. Spoon reserved mustard mixture onto salmon, spreading evenly; cover grill. Cook 10 to 15 minutes or until fish flakes easily with fork. Serve mayonnaise-mustard sauce mixture with salmon.