Add ground chicken and break up with a spatula until cooked through.
Add chopped onion & garlic to ground chicken and cook for approximately 5 minutes or until onion is translucent.
In a small bowl, whisk together hoisin sauce (or Aldi's Thai Red Sauce), soy sauce, sesame oil, vinegar, ginger, and sweet chili sauce (I omitted the sweet chili sauce based on my personal taste preference).
Pour whisked mixture over cooked chicken mixture and stir well.
Simmer over medium heat for 5 minutes.
Add chopped water chestnuts to mixture and stir.
Remove from heat and place 1/4 cup amounts of mixture into each lettuce leaf.