Make the Hoisin Sauce and set aside. Separate your lettuce out to individual leaves. Wash and dry your lettuce.
To a pan over medium heat add olive oil and chicken. Crumble your chicken up. Cook for 2 minutes then add in onion. Cook until the chicken is no longer pink, and your onions are soft. This will take about 5 minutes. Drain the excess fat.
Add in water chestnuts and half of the green onions. Cook for a minute. Add in half of the hoisin sauce. Cook for an additional 2-3 minutes, just until the sauce is thickened.
Fill your lettuce with 1/4 cup of the chicken filling and top with extra sauce.
Enjoy!