Slit the shrimp open along the underside, remove the 'sand vein' if necessary, and then butterfly and flatten, belly side down with the palm of your hand.
Strew the white and light green parts of the scallion over the bottom of a suitable steaming dish along with the ginger, lay the shrimp over top, and then splash on the soy sauce;
Steam the shrimp over high heat for about 5 minutes or so until all of the shells are pink.
Put the oil in a small pan, and heat until the smoking point. Scatter the scallion greens over the shrimp and drizzle over enough hot oil (at the table if desired) to sizzle the shrimp and the aromatics.