PLACE THE FISH ON A PLATTER large enough to hold it, and sprinkle it with salt. Squeeze the chunk of ginger in your hand to extract the juice, letting it sprinkle over the fish. (The ginger must be fresh and you must have strong hands to do this; as an alternative, use a garlic press.) Chop the garlic and fermented black beans together. Don't chop too fine or the mixture will become a paste and turn bitter. Scatter the beans, garlic, shredded scallions and shredded ginger over the fish. Mix the soy sauce, rice wine and sugar. Pour it over the fish. If the plate is too long to fit in a bamboo steamer or a wok, improvise a steamer. For example, a roasting pan could serve the purpose, with a trivet standing in the middle to hold the plate. Set the plate on the trivet. Pour boiling water into the pan, but not enough to reach the plate. Cover the pan with aluminum foil and crimp the edges to seal it. Put the pan over low heat to keep the water simmering. A fish 3 cm thick at its widest point will take 10 minutes in the steamer. (The covered pan can also be placed in a 200ºC oven to cook for the same length of time.) When the fish is done, remove the plate from the steamer. A thin sauce will have formed on the plate. Heat the peanut oil and sesame oil in a small saucepan almost to the smoking point, and pour the mixture over the fish.