Preheat broiler. Line rack of broiler pan with foil and lightly coat with non-stick spray.
Pat fish dry. Sprinkle fish with salt and pepper, then broil 4 inches from heat for 7 minutes. Cover fish loosely with foil and continue broiling 7 to 9 minutes or until salmon is a light pink throughout and flakes easily.
While salmon broils, whisk together all sauce ingredients in a bowl until combined. Serve salmon topped with kefir sauce.