Pick leaves from half the coriander and reserve. Finely chop remaining coriander.
Heat oil over high heat in a wok or large frying pan. Add mince and garlic and stir-fry for 5 minutes, breaking up lumps, or until browned and liquid has evaporated. Transfer to a bowl. Stir in onion, fish sauce and lime juice and toss well to combine. Add chopped coriander and a little each of the mint and chilli, reserving some for garnish.
Spoon mixture into lettuce leaves, garnish with reserved herbs and chilli, and shallots. Serve immediately with lime wedges.