Preheat oven to 400 degrees. Rinse fish in cool water and dry. Tuck the slices of ginger into the cavity of the fish. Spread a layer of salt about 3/4-inch thick on the surface of a large baking sheet or other ovenproof container. Wrap fish entirely in the nori, set it on top of the salt, and then use remaining salt to bury the fish completely. Bake 30 to 40 minutes, until fish reaches an internal temperature of about 130 degrees (use an instant-read thermometer, and poke it through the salt crust into the fish). Remove from oven and let rest 5 to 10 minutes (fish will continue to cook). Meanwhile, mix together the soy sauce, lime juice, ginger, and about a tablespoon of the scallions. Carefully remove the fish from its salt bed, set it on a work surface, and remove nori wrap. Set fish on a serving platter, scatter the remaining scallions over the surface, and serve immediately with the sauce alongside.
From "Salt and Pepper: 135 Perfectly Seasoned Recipes", by Michele Anna Jordan Broadway Books, 1999