Rinse the mussels under cold running water and scrape off any beards. Discard any that are open or that do not close when sharply tapped. Drain and set aside.
Heat the oil in a large saucepan, add the onion, garlic, chillies and turmeric and fry for 2–3 minutes. Add the mussels, vinegar, coconut milk, sugar and coriander. Stir well and bring to the boil.
Cover and cook gently for 5–6 minutes or until all the mussels have opened. Discard any that remain shut.
Transfer the mussels to a serving bowl with a slotted spoon, season the cooking juices and pour over the mussels. Garnish with grated coconut and serve with crusty white bread to mop up the juices.