Rinse the Japanese rice until the water runs clear. Cook in the rice cooker.
While the rice cooks, soak the black fungus in hot water until softened and doubled in volume. Drain and chop.
Take the cooked rice and spread on a tray. Use a fork to fluff it up. Cool completely.
Mix all the ingredients together except for the lettuce.
With wet hands (to prevent the rice from sticking on your skin) or using an onigiri molder, shape the rice mixture into balls or flattened triangles (or whatever shape you prefer, really).