1.Place prawns, birdseye chilli, coriander, fish sauce, brown sugar and half of the lime juice in a bowl. Toss to coat prawns all over Cover and refrigerate.
2.Meanwhile, make salsa. In a bowl, combine mango, long red chilli, onion and remaining lime juice and season. Cover with plastic wrap and set aside.
3.Preheat an oiled chargrill or barbecue grill on high. Thread prawns onto bamboo skewers (2 or 3 on each) and cook for 3-4 minutes each side, brushing with marinade, until cooked.
4.Divide watercress, avocado and cucumber between serving plates. Garnish with lime and mint, top with prawns and serve salsa in small bowls to side of prawns.
To dice the mango, cut the cheeks from each side of the pit. Using a large spoon, scoop the flesh from the skin of each half. Slice the flesh first horizontally then vertically to dice. Don’t waste the flesh left on the pit – eat it Aussie style and let the juice drip down your hands! Soak bamboo skewers for 30 minutes in cold water before using to avoid burning while cooking.