Heat sesame oil in a pan over medium heat. Add diced onions and cook until softened. Add ground chicken and cook until browned, breaking it up as it cooks.
Stir in minced garlic, hoisin sauce, soy sauce, rice vinegar, and grated ginger. Let it simmer for a few minutes until everything is well combined and the chicken is fully coated.
Add the chopped water chestnuts to the chicken mixture for extra crunch. Stir well and cook for another 2-3 minutes. For another great chicken dish, try these Sausage Cream Cheese Crescents.
Wash and dry the lettuce leaves, keeping them whole. Spoon the cooked chicken mixture into the center of each leaf.