Heat the oil in a wok over a high heat until the oil starts to simmer. Add the steak and curry paste, stirring to coat the beef, and stir-fry for about 2 minutes, until the beef is lightly golden but still pink in the middle.
Pour in the coconut milk and stock and add the sugar, ginger, lemon grass, mangetout, beansprouts, fish sauce and lime rind. Bring to the boil, then reduce the heat and simmer for 2 minutes, until the mangetout are tender.
Remove the ginger and lemon grass from the curry and stir in the coriander. Serve with rice, if liked.