First, heat 1 tablespoon of cooking oil in a skillet over medium heat and cook the chicken until it is no longer pink. Make sure the chicken crumbles in small pieces.
Add the garlic when chicken is almost done.
While the chicken is cooking, cover the dried mushroom with hot water and let sit for 5-10 minutes.
Remove and squeeze out any excess water. Remove the tough stems and chop.
When the chicken is done, add the mushrooms and water chestnuts and cook for 30 seconds.
Then add the hoisin sauce, soy sauce, vinegar, sesame oil, and chili garlic sauce.
Mix well and cook for another 1-2 minutes, until thickened.
Garnish with green onions. Serve with the butter lettuce.