1. Preheat the oven to 350°F. Make cuts in the fish, about 1 inch apart, through the flesh and down to the bone, from the gills' to the tail. Do this on both sides of the fish.
2. In a small bowl, combine the soy sauce, sherry, green onions, ginger, garlic, and sugar. Place the fish in a buttered 8" x 8" x 2" baking dish, and sprinkle the mixture evenly over the fish. Bake, uncovered, for 20 minutes or longer, depending on the thickness of the fish. When the fish flakes easily when tested with a fork, it is done. Serve with Brussels Sprouts with Walnuts.