1 red chilli, deseeded, plus 1 tsp chopped to garnish
2cm/¾in piece of root ginger, peeled and roughly chopped
juice of 3 limes and 1½ oranges
For the salad
1 small watermelon, weighing about 1.8kg/4lb
24 large cooked and peeled tiger prawns
4 spring onions, finely sliced
2 trimmed stems of lemongrass, finely sliced
4cm/1½in root ginger, peeled, cut into fine matchsticks
zest of 1 lime
3 lime leaves, shredded (optional)
a handful each of coriander and mint leaves, chopped
100g roasted salted peanuts or cashews, to garnish
Three hours before serving: make the dressing. Put the garlic and coriander in a food processor with 1 tsp salt and the sugar, then pulse to a pulp. Add the chilli, ginger and citrus juices and pulse until smooth. Cover and chill.
Two hours before serving: cut the watermelon into segments, remove the skin and seed the flesh. Cut into lozenges about 3cm wide.
Mix the melon and prawns and add the spring onions, lemongrass, ginger, lime zest and lime leaves. Chill.
To serve: toss the dressing and herbs into the salad and scatter with chilli and peanuts.