Cut whole leaves from the lettuce head to form cups (trim if needed).
In a bowl, mix together oyster sauce, soy sauce, sesame oil, cornflour, chilli and egg - set aside.
Heat oil in large frying pan over high heat, add ginger and garlic and cook for 1 minute. Add pork and cook, stirring to break up any clumps, until brown and cooked. Drain off any liquid.
Return pan to heat and add water chestnuts and noodles and cook for 4 minutes. Stir in the oyster sauce mixture and cook for 10 minutes or until sauce has thickened. (this is where I usually taste and add more chilli and any of the sauces you think it might need) Leave the mixture to cool slightly.
Put pork mix in middle of table, along with spring onion and hoisin sauce and let everyone help themselves to fill their lettuce leaf cups. Delicious but slightly messy and fun!