Whisk first 6 ingredients in 13x9x2-inch glass baking dish to blend for marinade.
Add salmon; turn to coat. Cover and chill at least 30 minutes and up to 2 hours.
Preheat broiler. Line heavy large baking sheet with foil; spray with nonstick spray.
Remove salmon fillets from miso marinade; using rubber spatula, scrape off excess marinade. Arrange salmon, skin side up, on prepared baking sheet. Broil 5 to 6 inches from heat source until skin is crisp, about 2 minutes. Using metal spatula, turn salmon over. Broil until salmon is just cooked through and golden brown on top, about 4 minutes.
Transfer salmon to plates, skin side down. Spoon Cucumber Relish over.
Sprinkle with sesame seeds, then sprouts and nori.
Serve immediately.
*White miso, mirin, and nori (thin sheets of dried seaweed) are available at Japanese markets and in the Asian foods section or refrigerated section of supermarkets.