MIX Mustard, sugar, water, oil, and garlic powder in a small bowl. Reserve 2 tablespoons of mixture. Set aside.
PLACE salmon in a large resealable plastic bag or glass dish. Add remaining marinade; turn to coat well. Refrigerate 30 minutes. Remove salmon from marinade. Discard any remaining marinade.
GRILL salmon, skin side down, over medium heat 15 to 20 minutes or until fish flakes easily with a fork. Brush with reserved marinade mixture during last few minutes of cooking. Sprinkle with parsley and serve with lemon wedges, if desired.