Make 3–4 deep diagonal slashes in the sides of the fish with a sharp knife. Rub the salt into the slashes and inside the cavity. Place the fish on a heatproof plate that will fit inside a steamer and scatter the ginger over the top.
Place the plate in the steamer, cover and steam for about 12–15 minutes until the fish is just cooked through – the flesh should be opaque in the centre and slightly flaking but still moist. Remove the plate from the steamer and drain off any liquid from around the fish. Transfer to a warmed shallow serving plate. Scatter the spring onions and chilli over the fish, then drizzle with the dark and light soy sauces.
Heat the oils together in a small saucepan until smoking, then drizzle over the fish. Serve with boiled rice.