In a large resealable plastic bag, combine the brown sugar, mustard, soy sauce and ginger; add the salmon. Seal bag and turn to coat; refrigerate for 30 minutes, turning occasionally.
Drain and discard marinade. Place salmon on a foil-lined baking sheet coated with cooking spray. Broil 4-6 in. from the heat for 7-9 minutes or until fish flakes easily with a fork, sprinkling with walnuts during the last 2 minutes of cooking.