In a small bowl, combine all sauce ingredients and stir until blended. If the mixture is too thick, add a splash of water for a smoother consistency.

In another bowl, dissolve the cornstarch in a bit of cold water and set aside.

Heat the oil in a wok or skillet over medium-high heat. Add the diced onion and cook until translucent (about 3-4 minutes). Then, add minced garlic and grated ginger; sauté until fragrant (about 30 seconds).

Stir in the five-spice powder, then add the ground chicken. Break it into pieces as it cooks, stirring frequently, until browned and cooked through (about 5-7 minutes).

Pour in the sauce, stirring well to coat the meat and cook until slightly thickened (about 2-3 minutes). Add the diced carrots and water chestnuts, stirring until evenly incorporated.

Increase the heat to high, constantly stirring until the filling is well-coated and heated through (about 2-3 minutes). Optionally, add black soy sauce for an extra depth of flavor.

Mix in the cornstarch slurry to thicken the mixture. Remove from heat and stir in the chopped green onions.

Lay out the lettuce leaves, add a layer of hoisin sauce if desired, and spoon in the chicken mixture. Garnish with sesame seeds for extra crunch and presentation!