1.Preheat oven to 180°C.
2.In a large bowl, combine fish sauce, juice and chilli flakes.
3.In a small bowl, combine beetroot and 1 tbsp of the dressing. In a medium bowl, combine carrot, snake beans and 2 tbsp of the dressing. Remove seeds from cucumber; cut into 5mm pieces. In a large bowl, add cucumber to remaining dressing. Cover each bowl with plastic wrap; stand vegetables 15 minutes.
4.Meanwhile, place rice on an oven tray; roast 12 minutes or until golden. Process rice in a small food processor (or crush with a mortar and pestle) until very finely chopped.
5.Add tomatoes to cucumber mixture with onion, herbs, ground rice, carrot mixture and half the nuts. Strain beetroot mixture through a sieve, add to larb; toss gently to combine.
6.Serve larb with lettuce leaves, sprinkled with remaining nuts.
You will need about half a small bunch of snake beans.Note