In a 9 x 9-inch baking dish, combine the ground ginger, grated ginger, miso paste, sesame oil, soy sauce, vinegar, and brown sugar until smooth.
Pat the salmon dry and place, skin side up, in the marinade, spooning some marinade over each filet. Cover and refrigerate for 1 hour.
Turn the oven broiler to HIGH with a rack in the top third of the oven.
Remove the salmon from the marinade, allowing any excess marinade to drip off, and arrange, skin sides down, on a rimmed sheet pan. Broil until the edges are crisp and the salmon flakes easily with a fork, about 10-12 minutes.
Serve the salmon topped with green onions and sesame seeds.