Core the lettuce, separate whole leaves, rinse, pat dry, and chill in a towel-lined container.

Drain and mince the water chestnuts. Finely mince the mushrooms. Peel and mince the garlic. Grate the ginger. Slice the green onions into thin rings.

Whisk the stir-fry sauce ingredients in a small bowl until glossy and dark brown. Stir the dipping sauce ingredients in a second bowl until the sugar dissolves.

Heat oil in a large wok until shimmering. Add garlic and ginger and stir until pale gold and fragrant.

Add mushrooms with a pinch of salt. Stir until their moisture cooks off and they turn deep golden-brown and shrunken.

Add water chestnuts and toss briefly, then scoop the vegetables into a bowl and set aside.

Place ground chicken in the hot wok. Break into small crumbles with a splash of soy sauce. Cook until opaque white, lightly golden at the edges, and no pink remains.

Return the vegetables to the wok. Pour in the stir-fry sauce. Simmer a few minutes until the sauce reduces to a thick glossy glaze that clings to the filling.

Fold in the sliced green onions.

Arrange chilled lettuce cups on a platter. Spoon filling into each cup. Top with crispy chow mein noodles and remaining green onions. Serve with the dipping sauce.