Place half the spring onions and all the ginger into a bowl.
Set the remaining spring onions aside.
Pour the soy sauce and sherry over the spring onions and ginger.
Place the fish skin side up on a board and make six small incisions into each.
Place the banana leaves into the steamer and place a piece of sea bass on top of each piece of leaf. (If you have a large steamer you should be able to fit 3 in each steamer layer.)
Spoon the spring onion mixture over the top.
Place the lid on the steamer and set over a saucepan of boiling water.
Steam for 6-7 minutes until just cooked through.
Meanwhile, heat the groundnut oil in a wok and stir-fry the Chinese greens until tender.
Finally, heat a frying pan until hot, and add the sesame oil and heat until just smoking.
To serve, place the greens onto a plate, top with the fish, and remaining spring onions, then pour over the hot sesame oil.