Combine lime juice, fish sauce, sugar and chilli in a large bowl.
Cook noodles following packet directions. Drain and immediately add to dressing in bowl. Toss well to coat (this will stop the noodles from sticking together). Add onion, coriander, mint, basil, chicken and prawns. Toss gently to combine.
Place lettuce over the base of a serving platter. Top with noodle salad and sprinkle with shallots. Sprinkle with extra coriander, mint and basil. Serve with lime wedges.