Peel and finely chop the garlic, ginger and shallots, trim and chop the spring onions into 2cm pieces, and prick the chillies.
Roughly chop the fish and place in a bowl to marinate with 50g of the sugar, the fish sauce, garlic, ginger, shallots, spring onions, chillies and a pinch of ground black pepper.
Meanwhile, make some caramel. Place the remaining sugar in a heavy-bottomed saucepan with 100ml of water and bring it to the boil over a medium heat. Don’t stir it, just swirl it occasionally. Keep it boiling for about 10 minutes, or until you have a gorgeous golden caramel liquid.
Now cook the fish. Place a clay pot or earthenware dish on a medium heat and add a splash of groundnut oil. Add the fish, reserving the marinade juices, and seal all the sides for 2 to 3 minutes altogether.
Pour in the marinade, the caramel and the coconut water. Gently bring it to the boil, then let it simmer uncovered for 15 to 20 minutes, or until the fish is cooked through and the sauce is reduced, golden and sticky. If it looks too dry halfway through, add a little more coconut water.
Serve immediately – delicious with steamed jasmine rice and greens.