1. In blender, combine all ingredients except salmon and watercress until smooth.
2. Place salmon on nonstick baking sheet. Brush both sides of each fillet evenly with black bean mixture. Cover and refrigerate at least 2 hours.
3. Preheat broiler, or prepare outdoor grill. Broil salmon 2 minutes; turn and broil until fish is opaque and flakes easily when tested with fork, 2 to 3 minutes.