In a small bowl, whisk together the soy sauce, hoisin sauce, rice vinegar, sesame oil, oyster sauce, brown sugar, sriracha (if using), cornstarch, and water until smooth. Set the sauce aside while you prepare the filling.

Heat the vegetable oil in a large skillet over medium-high heat. Add the ground chicken and cook for about 5–6 minutes, breaking it into small crumbles with a wooden spoon until fully cooked and lightly browned.

Stir in the diced mushrooms, chopped water chestnuts, minced garlic, grated ginger, and sliced green onions. Cook for another 3–4 minutes until the vegetables soften and become fragrant.

Pour the prepared sauce into the skillet. Stir continuously until the sauce coats the chicken evenly and thickens slightly, creating a glossy, flavorful filling.

Reduce the heat to low and let the mixture simmer for 2–3 minutes. This allows the flavors to blend together while the sauce fully coats every bite of the filling.

Carefully separate the lettuce leaves and wash them thoroughly. Pat them completely dry with paper towels to keep them crisp.

Spoon a generous amount of the warm chicken filling into each lettuce leaf. Garnish with sliced green onions, sesame seeds, crushed peanuts if desired, and a squeeze of fresh lime juice. Serve immediately while the filling is warm and the lettuce is crisp for the best texture and flavor.