Peel and chop the garlic: you should have about ½ cup. Place into a small saucepan with the oil and salt over a low heat. Stir occasionally as mixture comes barely to a simmer, then cook for about 30 minutes, or until garlic is soft and a pale golden colour. Add juice from one lime and continue to cook for a further 5 minutes. Remove seeds from chillies, cut into thin strips and add to oil. Add salt to taste. Keep mixture warm while preparing the prawns.
Peel and devein prawns. Place a large frying pan over a medium-high heat with 1½ tbsp of the garlic and chilli oil (using the oil only and leaving out any solid pieces of garlic and chilli). Add half the prawns, season with salt and pan-fry until just cooked, about 3-4 minutes. Remove from heat and stir through 1 tbsp of chopped coriander. Repeat with remaining prawns.
Put prawns on a platter. Use a slotted spoon to scoop out the warm bits of garlic and chilli and heap them over the prawns. Finish with a sprinkling of parsley and coriander and serve with wedges cut from the remaining limes.
Keep any leftover garlic and chilli-infused oil for future use.