Heat the oil in a large frying pan over a medium heat. Add the curry paste and cook, stirring, for 1 minute. Stir in the chicken and onion, cook for 3 minutes, then add the beans and stock. Simmer for 3 minutes, then add the pak choi leaves.
Stir in the coconut milk, then reduce the heat a little and simmer for 3 minutes, or until the chicken is cooked through with no pink meat showing. Stir through the soy or fish sauce and scatter over the coriander.
Meanwhile, put the rice in a pan with 320ml (11fl oz) salted cold water. Bring to the boil, then cover and simmer for 10 minutes. Remove from the heat and set aside for 5 minutes, covered. Serve the rice with the curry and lime wedges for squeezing over.