Arrange 1/2 of the spring onions on the bottom of the steamer insert. (If possible, steam in a bamboo basket in order to retain the steam and juices around the fish). Place half of the mushrooms and cabbage on top of the onions. Place fish on top of the vegetables. Sprinkle ginger, garlic and crushed chillies over fish. Top with the remaining spring onions, mushrooms and cabbage. Drizzle soy sauce and water over everything.
Place steamer insert or bowl into steamer over 5cm of boiling water, and cover. Steam for 15 to 20 minutes, or until fish flakes easily. Garnish with coriander, if desired.