Soak the dried rice noodles in boiling water for 5 minutes. Drain, rinse, drain again and place in a large bowl with the cucumber, cut into long thin strips, and the cooked, peeled tiger prawns.
In a food processor, blitz a small handful each of coriander and mint leaves, the olive oil, finely grated zest and juice of a lime and crushed garlic clove until fairly smooth. Season and toss with noodle mixture. Serve in iceberg lettuce leaves.