Cut the pork into thin strips about 5cm/2in long. In a medium bowl, combine the marinade ingredients. Add the pork, mix well and leave to marinate at room temperature while you prepare the other ingredients. Drain, discarding the marinade.
Heat a wok over a high heat until it is hot. Add the oil, and when it is very hot and slightly smoking, add the garlic and stir-fry for 15 seconds or until golden brown.
Add the pork and stir-fry for 3 minutes.
Finally, add the pineapple, coriander, soy sauce and sugar and continue to stir-fry for 3 minutes.