In a small bowl, combine hoisin sauce, soy sauce, rice wine vinegar, Sriracha, and sesame oil.
Set your Crockpot Express to Sautee, heat olive oil. Add onions and cook until soft, 5 minutes, then stir in garlic and ginger and cook for one minute. Add ground chicken and cook until cooked through- will be white
Pour in the sauce mixture and cook 1 to 2 minutes more, until sauce reduces slightly and chicken is cooked through completely. Turn off heat and stir in chestnuts and green onions. Season with salt and pepper.
Scoop about 1/4 cup of chicken mixture into center of each lettuce leaf. Serve immediately.