Soak the mushrooms in hot water for 20 minutes. Drain and finely chop, discardint the hard stem.
Heat half the oil in a wok and stir-fry the pork, chicken, garlic and ginger until the meat changes color, breaking up the lumps. Add the cerlery, beans, red pepper and cook for 3 minutes. Add the water chestnuts, oyster, soy sauce, sugar, and salt and pepper.
To serve, tear the lettuce into cups and place heaped tablespoon of the filling into each cup. Roll up and eat with your fingers.