Dice the chicken into tiny bite sized pieces and mix together in a bowl with first 4 ingredients: sherry, soy sauce, sesame oil and corn starch. Refrigerate for 15 minutes.
Whisk together all the sauce ingredients in a small bowl and set aside.
Follow instructions on the package for cooking the noodles or try the following method. Boil 6-8 cups of water in the kettle and pour into a large bowl. Break up noodles with your hands to about 5 cm size pieces and add to the water. Let sit for 3-4 minutes and rinse under cold water and set aside.
Prepare all the vegetables. Finely dice celery and carrots, remove the stems from the mushrooms and thinly slice, and chop the water chestnuts into small pieces as well. Thinly slice the green onions separating the white part from the green. Wash and finely chop the fresh mint. Mint and green onion parts can be set aside in a bowl for the garnish.
Heat 1 tablespoon of canola oil in a large frying pan or brasier over medium high heat. Add the chicken and cook stirring often for about 5 minutes until chicken is slightly brown and cooked through. Set aside in a bowl.
Add the remaining 1 tablespoon of oil and cook celery, carrots, cabbage and mushrooms until celery is tender crisp and mushrooms have cooked down about 5 minutes. Add white parts of the green onion, water chestnuts, garlic and ginger. Stir constantly and cook for another minute.
If preparing ahead of time. Return chicken to the pan and toss with vermicelli and sauce but do not re-heat until you are ready for dinner.
Just before dinner heat thoroughly. Spoon into lettuce leaves and sprinkle with mint and green onions.
Serve with hoisin sauce.