Begin by dicing red bell pepper, mushrooms, and water chestnuts (unless you bought pre-diced). Mince garlic. Set aside.
In a small bowl, whisk together the hoisin sauce, soy sauce, and black pepper.
Add sesame oil to a large skillet or wok set over medium-high heat. Add garlic and saute for 1 minute. Add ground turkey and cook for 5 minutes, using a spatula to crumble the meat. Add the mushrooms, and red bell pepper and saute, stirring frequently, until the turkey is no longer pink and the mushrooms and red bell pepper have begun to soften.
Add the sauce mixture and water chestnuts to the pan and stir to coat all ingredients. Cook for 3 minutes to allow the sauce to thicken slightly.
To serve: Rinse lettuce and pat dry. Divide lettuce leaves among plates. Spoon a small amount of the filling into each lettuce leaf and fold to eat. Enjoy!