Bring small amount of water to a boil over high heat in steamer large enough to fit bowl without touching sides of steamer.
Carefully place bowl in steamer, cover, reduce heat to medium and steam just until custard is set and barely trembles when bowl is touched, 10 to 13 minutes.
Check water level occasionally and replenish as needed with boiling water.
Carefully remove bowl from steamer. Pour soy sauce over custard.
In small skillet, heat oil over high heat until hot but not smoking.
Carefully drizzle hot oil over custard (you will hear it crackle).
Garnish with cilantro and scallions and serve at once.