In a medium saucepan combine miso, vinegar, 1/2 cup brown sugar, and 1/3 cup water. Cook over medium heat, stirring occasionally, until miso and sugar have dissolved; cool to room temperature. In a resealable plastic bag combine salmon and miso mixture. Marinate in the refrigerator for at least 2 hours.
Meanwhile, in a blender, combine cilantro, lime juice, shallot, chili, garlic, ginger, oil, and remaining teaspoon of brown sugar. Blend until mixture is smooth.
Heat broiler with the rack in the highest position. Lift salmon from marinade; broil salmon until cooked through, about 10 minutes. Serve with cilantro sauce.