Combine garlic, onion, hoisin sauce, soy sauce, rice wine vinegar and ginger in a large bowl.
Add in the chicken and use your hands to work the sauce into the meat.
Heat olive oil in a saucepan over medium high heat.
Add the chicken mixture and cook until browned, about 5 minutes.
Stir in the water chestnuts and cook for an additional 2 minutes.
If you have fat in the pan, drain the cooked chicken on paper towels before seasoning with salt and pepper.
Clean your lettuce and place the individual large leaves on your serving plate. Place about 3 tbsps of the chicken in the center of each lettuce leaf and garnish with chopped green onions.