Cook the beans in boiling water for 3 minutes, remove with a slotted spoon and cool under cold water. Add the beansprouts to the same water and blanch for 30 seconds, drain and cool under cold water. Place both in a large bowl.
Add the carrot, Walnuts, chilli and papaya to the bowl.
Whisk together the lime zest and juice, fish sauce, oil and sugar and toss into the salad.