Heat half the oil in a wok over high heat until just smoking. Add half the pork mince, lemon grass and chilli and stirfry, breaking up any lumps, for 34 minutes or until pork changes colour. Transfer to a heatproof bowl. Repeat with the remaining oil, pork, lemon grass and chilli, reheating the wok between batches. Set aside for 15 minutes to cool slightly.
Whisk together the lime juice, fish sauce, sweet chilli sauce and lime rind in a small bowl until well combined. Drizzle the pork mixture with the dressing. Add the onion, coriander and mint and stir to combine. Spoon the pork mixture among lettuce leaves and sprinkle with peanuts to serve.