Set up a steamer: a wok or wide pot with 2 inches of water, a trivet or steamer rack, and a lid that closes. Bring the water to a full boil before the fish goes in — the fish should meet full steam, not a warming pot.
Pat the fillets dry. Season lightly with salt. Lay half the ginger and the 2-inch scallion pieces on a heatproof plate; set the fillets on top (this lifts the fish so steam circulates underneath). Scatter the remaining under-fish ginger over the top. Drizzle with the Shaoxing wine, if using.
Set the plate in the steamer, cover, and steam over medium-high heat for about 9 minutes for 1-inch fillets.
Check doneness with an instant-read thermometer in the thickest part of the largest fillet: it must read 145°F (63°C) (FoodSafety.gov safe minimum for fish). The flesh should also flake easily and look opaque throughout. If under, steam 2 minutes more and re-check. Do not serve on time alone.
While the fish steams, stir the soy sauce, sugar, and sesame oil together in a small bowl.
Transfer the fish to a serving plate; discard the steamed ginger and scallion pieces underneath (they have done their job). Top with the fresh scallion strips and any remaining fresh ginger.
Heat the 2 tbsp neutral oil in a small pan until very hot and just starting to shimmer. Pour it slowly over the scallions and ginger on the fish — keep your face and hands clear; it will sizzle.
Spoon the soy mixture around (not over) the fish. Serve immediately with rice.