How to Make It
Heat 1 tablespoon of the peanut oil in a small skillet. Add the onion and a pinch of salt and cook over high heat, stirring once or twice, until browned, about 2 minutes. Transfer to a small bowl and stir in the ginger.
In a large wok, set a round rack that will sit at least 3 inches above the bottom. Add 2 inches of water and bring to a boil. Set the fish on a heatproof plate that will fit in the wok and sprinkle the onion and ginger on the fish. Set the plate on the rack, cover the wok and steam the fish over moderate heat until just cooked through, about 20 minutes.
Drizzle the fish with soy sauce. In a small skillet, warm the remaining 1 tablespoon of peanut oil with the sesame oil over moderately high heat, then pour it over the fish. Sprinkle with the cilantro and scallion and serve.