Rinse fish inside and out under cold running water. Pat dry. Rub cavity and exterior with salt.
Place 4 spring onion stalks equidistant and parallel to one another. Place fish on top. Place ginger slices in cavity.
Fill wok with 3-5cm water. Place wire rack stand into centre of wok. When water is boiling, place steam plate on stand. Cover tightly and adjust to medium high heat. Steam timing differs - ~8 minutes for 250g fillet, ~13 minutes for 800g whole fish.
Mix the light soy sauce, castor sugar, and water together on medium high heat until sugar dissolves. Set aside.
Place oil in saucepan. Heat until it smokes.
Insert metal skewer or metal chopstick into various parts of the fish and leave it for 5 seconds. Pull out and feel for the temperature. It should feel warm. Cook longer if the skewer feels cold.
Once fish is ready, discard steaming liquid and ginger slices. Garnish with coriander, chopped spring onion stems, shredded ginger. Drizzle cooked sauce and heated oil all over fish and serve.
During steaming, the water should be at a slow boil that generates a good amount of steam, but not so high that the water evaporates too quickly.
To check if the fish is cooked, insert a chopstick into the middle of the thickest part of the fish. If the chopstick pierces through the fish easily, it is usually fully cooked. Remove the fish.