Several hours ahead, combine mustard seeds and sour cream (to soften seeds prior to cooking). Preheat broiler. Line baking pan with foil, and coat with cooking spray. Place salmon pieces, skin-side down, on prepared pan. Season with salt and pepper. Combine mustard and lemon juice with sour cream and mustard seeds. Spread evenly over salmon.
Broil salmon 5 inches from heat until opaque in center, about 10-12 minutes. Serve immediately. 4 servings.