Heat the oil in a nonstick frying pan, add the chicken and fry for 2 minutes.
Add the curry paste and continue to fry for 1 minute, then add half the coconut milk, bring to the boil and simmer gently for 10 minutes.
Meanwhile, put the rice in a saucepan with the remaining coconut milk and 100 ml (3½ fl oz) water. Bring to the boil, then reduce the heat, cover and simmer for 10–12 minutes until the liquid is absorbed, adding a little extra water if necessary. Turn the heat off and stir in the coriander.
Put chicken and spring onion slices and some rice on a lettuce leaf and squeeze the lime wedges over the filled shells before eating.