step 1
In a large saucepan, bring 2 litres of water and a large pinch of salt to the boil. Add the prawns and cook for 2 minutes maximum, then remove with a slotted spoon and immediately transfer to a bowl of iced water to prevent further cooking (and turning the prawns rubbery). Drain well, then place in a bowl (not a metal one) and add the lemon and lime juice, mixing well.
step 2
Add the red onion and chilli, stirring to combine. Cover and refrigerate for 30 minutes.
step 3
Remove from the fridge and add the avocado, cucumber and coriander or parsley. Season with salt and pepper, mix well, then spoon into attractive dishes or glasses and serve.