Step 1

Make the sauce. Place 3 tablespoons of the hoisin sauce, soy sauce, rice vinegar, and sesame oil in a small bowl and whisk. If you'd like a more thickened, glossy sauce, whisk in the cornstarch; place near the stove.

Step 2

Cook the ground chicken. Heat 1 teaspoon of the oil in a large frying pan over medium heat until shimmering. Add the ground chicken and cook, breaking it up into small pieces, until cooked through and no longer pink, 7 to 8 minutes. Transfer the cooked chicken to a clean bowl; set aside.

Step 3

Cook the vegetables and aromatics. Add the remaining 1 teaspoon oil to the same pan. Add the mushrooms and any optional vegetables, and cook, stirring occasionally until tender, 4 to 5 minutes. Stir in the water chestnuts, garlic, and ginger, and cook until fragrant, about 30 seconds.

Step 4

Combine the vegetables and chicken. Return the chicken to the pan and add 1/2 of the scallions.

Step 5

Stir in the sauce. Add the sauce and cook, stirring occasionally, until bubbling and the sauce is warmed through, 30 to 60 seconds. Taste and add more hoisin sauce if desired.

Step 6

Serve with the lettuce. Break off all the lettuce leaves and pile them on a plate in the center of the table, along with small dishes with hot sauce, red pepper flakes, and the remaining scallions. Transfer the hot chicken mixture to a serving dish, or serve straight from the skillet. Give everyone a spoon and let them dig in — place a generous spoonful of chicken mixture in the middle of a lettuce leaf, top with scallions and hot sauce or red pepper flakes, and eat right away.