Heat a large non-stick frying pan over medium-high heat. Add pork mince, 1/4 of shallots and 1 tbs lime juice. Cook, stirring for 10 minutes until browned. Use a wooden spoon to break-up pork as it cooks.
Combine remaining shallots, lime juice, fish sauce, chilli sauce, mint and coriander in a large bowl. Add cooked pork mince and toss well to coat.
Spoon mince into lettuce cups with sliced cucumbers and serve.