Soak mushrooms in warm water to cover until softened, about 30 minutes; drain. Discard stems and mince caps.
Place mushrooms in a bowl with remaining ingredients; mix well. With wet hands, roll meat mixture into 24 balls, using 2 tablespoons for each. Drain rice and spread on a plate. Roll each ball in rice to coat completely. Arrange meatballs, without crowding, on two heatproof dishes.
Prepare a wok for steaming. Steam meatballs, one dish at a time, over high heat until pork is cooked through, about 25 minutes.
Recipe Notes
From Martin Yan’s Feast by Martin Yan, 1998 (Bay Books).