Heat oil in a wok over medium-high heat. Cook the onion, lemongrass, chilli, ginger and garlic for 1 minute or until fragrant.
Add the pork and cook for 4-5 minutes, until cooked through.
Add curry paste and cook, stirring, for 1-2 minutes, until fragrant.
Add the beans, fish sauce, lime juice and sugar, and cook, stirring, for 1-2 minutes or until the beans are just tender.
Stir in half the basil. Serve on rice noodles, topped with the remaining basil.
