Heat oil in a frying pan and fry the chopped onion. Then add in the minced pork and soy sauce, fry until the meat is no longer pink. Then add water chestnuts and stir-fry for a further 2 minutes.
Add shredded lettuce and cook for 1 minute or until the lettuce wilts slightly.
Add in chinese chives and toss gently.
Spoon 3-4 tbsp of pork mixture into each lettuce cup and serve hot.