Heat the oil in a large frying pan until very hot. Add the onion and fry briskly until lightly browned. Remove and drain off most of the oil.
Add the curry paste and lime leaves to the pan. Stir over a moderate heat for 2 minutes then add the chicken. Stir and cook for about 2 minutes.
Return the onions to the pan with all the remaining ingredients except the pineapple and coriander. Add barely enough water to cover then simmer, uncovered, for 10 minutes.
Add the pineapple and simmer for 2-3 minutes. Check seasoning, adding more fish sauce as needed.
Scatter with coriander and serve with thai fragrant rice.