If you are using frozen prawns, defrost them thoroughly.
Wash the prawns and pat-dry them with kitchen towel.
Squeeze the limes into a glass bowl, add the minced garlic and grated ginger. Add the finely chopped chili, then mix.
Add the prawns, mix thoroughly to cover each with the marinade, and rest for half an hour in the fridge.
Pour some oil into a wok and heat.
Mix the cornstarch with a little salt and coat the prawns in it, one at a time. Put them on a plate.
When the oil is hot and smoky, cook the prawns on both sides for 2-3 minutes (in several batches), until golden and crispy.
Drain them on a plate, lined with paper kitchen towel.
Serve them warm, sprinkled with chopped coriander and lime wedges & chilli sauce on the side.