Clean and rinse the fish and pat dry with paper towels. Make three or four diagonal slashes down to the bone on each side of the fish and gently rub with salt, inside and out. Put aside for 10 minutes.
Peel the ginger and cut into julienne strips, then trim the spring onions, cut into 7.5-cm lengths, slice them lengthways, then put aside. Stir the soy sauce and sesame oil together in a small bowl and put aside.
Fill a steamer or wok with water to a level of 5–7.5cm and bring to the boil. If using a wok, place a trivet in the bottom.
Rinse the salted fish under cold running water then dry with paper towels. Place on a heatproof plate and lower into the steamer basket or wok; do not let the plate touch the water. Cover, reduce the heat and steam gently for 15–20 minutes, or until the fish is cooked.
While the fish is steaming, seed the chilli and cut into fine shreds. Heat the oil in a small frying pan and cook the chilli and ginger over high heat until softened.
Transfer the fish to a warmed serving dish and sprinkle with the spring onions, ginger and chilli. Pour the soy sauce and sesame oil mixture over the top, garnish with coriander sprigs and serve immediately.