1. Finely chop the pickled chillies and add the rest of the ingredients to make the chutney.
2. For the sauce, mix all of the ingredients with 480ml of water in a small pan, bring to a simmer, then turn down the heat to low and bubble very gently for 30 minutes.
3. Dust the fish in the cornflour, making sure it is evenly coated. Put in on a plate and sprinkle over plenty of the chutney. Half fill a pan with just-boiled water and fit a large bamboo steamer on top that will fill the plate. Put the plate in the steamer, cover with the lid and steam for 8 minutes, then pour away the liquid.
4. Put the steamed fish and chutney on a serving platter, pour over the sauce and top with the spring onions. Heat the vegetable oil until very hot in a small pan, then carefully spoon it over fish and sauce. Scatter over the coriander and serve with steamed rice.