Cut the lemon grass into pieces approx 6 cm long. Place in a pan with the water and the tofu and slowly bring the water to the boil. Simmer gently for 5 minutes. Remove the pan from the heat and set aside to cool to allow the lemongrass flavour to absorb into the tofu.
Once cool, blot the tofu dry and blend in an processor until it resembles minced meat. Combine the kaffir leaves, nuts, fish sauce, papaya, herbs, chilli, cucumber and lime juice and mix through. Chill until you are ready to serve. Arrange a spoonful onto each leaf and serve.
Note: Betel leaves are used in South Asian cooking. Available from Asian markets the leaf is used in a number of traditional remedies for the treatment of stomach ailments, infections, and as a general tonic.
Makes 12 servings (serve = 1 leaf)