Soak the dried shiitake mushrooms in warm water for several minutes until softened. Once tender, remove the stems and chop finely. This gives your filling a meaty texture and deep, earthy flavor.
In a bowl, combine ground chicken, water chestnuts, mushrooms, soy sauces, oyster sauce, sesame oil, rice wine, sugar, and white pepper. Mix everything well and let it marinate for about 15 minutes to absorb the flavors.
In a small bowl, whisk together hoisin sauce, chili sauce, and warm water until smooth. Set it aside so it’s ready when serving.
Heat a drizzle of sesame oil in a large skillet or wok over medium-high heat. Add the chopped garlic and sauté briefly until fragrant, about 10 seconds. Then, add the marinated chicken mixture. Stir-fry for 4–5 minutes, breaking up the meat as it cooks, until fully done and slightly caramelized.
Lay the lettuce leaves flat on a serving platter. Spoon about ¼ cup of the chicken mixture into each leaf. Sprinkle with diced scallions and serve immediately with the hoisin dipping sauce. Eat them right away while the lettuce is still crisp!