Heat the oil in a saucepan, add the onion and red pepper and cook for 5 minutes until soft and just starting to brown. Add the chicken and cook for 5 minutes until browned all over.
Add the mangetout, curry paste, lemon grass, ginger, garlic and soy sauce and cook, stirring, for 2–3 minutes. Add the coconut milk and stir well. Cover and simmer gently for 5–8 minutes.
Remove from the heat, check and adjust the seasoning if necessary and stir in the basil just before serving with boiled basmati rice.