To make the dipping sauce, combine everything in a bowl and whisk together until combined. Set aside until ready to serve.
Whisk rice flour, egg, 1/2 teaspoon salt, and club soda in a large bowl until smooth.
Place green rice flakes in a shallow bowl.
Season prawns with salt and pepper and put them in a separate bowl.
Heat oil n a large saucepan to 350-375 degrees F.
Dip a prawn into the batter, roll it in green rice flakes until completely coated. Repeat with another two prawns.
Lower the prawns into the oil and fry for 2-3 minutes until golden. Remove the prawns from oil and drain on a plate lined with paper towel. Repeat with remaining prawns.
Serve immediately with lettuce, fresh herbs, and nuoc cham.