In shallow nonmetal dish, mix soy sauce, lemon juice, water, garlic powder and onion powder. Add salmon, skin side up. Let stand at room temperature 30 minutes to marinate.
Meanwhile, in small bowl, mix sauce ingredients. Cover; refrigerate until serving time.
Heat gas or charcoal grill. Brush skin side of salmon with oil. Place salmon, skin side down, on grill. Cover grill; cook over medium heat 13 to18 minutes or until fish flakes easily with fork. To serve, cut into 8 pieces. Serve with sauce.