Heat the oil in a frying pan and fry the garlic for one minute.
Add the spring onion, chilli, lime zest, prawn peelings and season with salt and freshly ground black pepper. Cook for a further minute.
Add the coconut milk and chicken stock and simmer for five minutes.
Pour the soup through a sieve. Discard the prawn shells but add the rest of the solid ingredients back into the soup.
Transfer the soup into a serving bowl and garnish with the coriander leaves to serve.