How to Make It
Wash the fish in cold water and wipe dry. Make 3 parallel diagonal 2-inch-long slashes on each side of the fish, slicing through to the bone. Rub the fish all over with 1 teaspoon of sea salt and lay it on a heatproof plate large enough to hold it.
In a mortar, pound the ginger to a paste with a pinch of sea salt. Take one-third of the ginger paste and stuff a little into each of the slashes in the fish. In a small bowl, mix the remainder of the ginger paste with the soy sauce, wine and 1/2 teaspoon of the sesame oil. Spoon the sauce into the cavity and on top of the fish and let marinate for 10 to 20 minutes.
Tuck one-fourth of the scallion shreds into the cavity of the fish. Spoon any marinade from the plate over the fish and top with the remaining scallions.
To set up your steaming arrangement, pour about 3 cups of water into a large wok and bring to a boil over high heat. Set the plate with the fish in a metal or bamboo steamer and cover tightly with a lid or with foil. When the water is boiling vigorously, put on oven mitts and carefully place the steamer in the wok; the water should not touch the plate. Steam the fish until it is opaque throughout and flakes easily when pulled with a fork, 15 to 18 minutes. Carefully remove the steamer from the wok.
When the fish is almost done, heat the peanut oil and the remaining 1/2 teaspoon of sesame oil in a small skillet until very hot. Remove the plate with the fish from the steamer. Pour the hot oil over the fish to glaze it (steaming often leaves a very matte finish) and serve the fish immediately from the plate. Guests can lift pieces of fish off the plate with chopsticks as they eat or they can be served formal portions. Be sure to serve a little of the sauce with the fish.