Dry the fish with paper towels. Rub both sides of the fillets with salt. Scatter the ginger over the top of the fish and place onto a heatproof ceramic dish.
Place the dish into a bamboo steamer set over about 5cm of boiling water, and cover. Gently steam for 10 to 12 minutes.
Pour accumulated water out of the dish and sprinkle the spring onion over the fish. Drizzle both soy sauces over the surface of the fish.
Heat peanut and sesame oils in a small frypan over medium-high heat until they begin to smoke. When the oil is hot, carefully pour on top of the halibut fillet. The very hot oil will cause the spring onions and water on top of the fish to pop and spatter all over - be careful. Garnish with coriander sprigs and serve immediately.