Add at least 1-2 inches of water to your steaming set-up. Bring to a boil.
While the water is coming up to a boil, arrange the fish on a heat-proof plate. Choose a dish that fits inside your steamer and has sides tall enough to contain the sauce and extra liquid.
Spread the ginger, garlic, and black beans evenly over the fish fillets.
Place the fish into the steamer.
Cover and steam for 7-10 minutes, depending upon the size/thickness of your fish fillets. If the fillets are smaller and thinner, you can cook for as little as 4-5 minutes. You can check if the fish is done cooking by piercing the thickest part of a fillet with a fork or butter knife. If the fish is fully cooked, it should flake apart easily. Adjust the cooking time as needed.
While the fish is steaming, mix the soy sauce, hot water, Shaoxing wine, sugar, and salt together in a small bowl until the sugar and salt dissolve. Set aside.
Once the fish has finished cooking, remove it from the steamer. *Note 2
Pour the prepared sauce over the fish. Arrange the sliced green onion on top.
Heat the 1 tbsp of oil in a saucepan just until it begins to smoke. Pour the oil over the green onion to release its aroma. Serve while warm.