For the prawns, pound the coriander and olive oil together in a pestle and mortar until the mixture is the consistency of pesto. Dip the prawns in the coriander to coat.
Unravel the pastry onto a flat, clean work surface. Cut the pastry into 12 equal pieces about 10cm/4in (keep the pastry pieces covered after you've cut them out to prevent them from drying out). Wrap the pastry pieces around the prawns.
Heat a deep fat fryer to 170C/325F/Gas 3, or until a breadcrumb sizzles and turns brown when dropped into it. (CAUTION: hot oil can be dangerous. Do not leave unattended.)
Deep fry the prawns in batches until golden-brown. Remove with a slotted spoon, drain on kitchen paper and keep in a warm place until ready to serve.
For the salsa, combine all of the salsa ingredients. Leave to stand for about 15 minutes to let the flavours infuse before serving.
Serve the prawns with the salsa on the side.