Lettuce Chicken Wraps

Ingredients

• ["1/4 cup oyster sauce", "1 tablespoon hoisin sauce", "1 tablespoon soy sauce", "2 teaspoons sesame oil", "2 teaspoons sugar", "2 teaspoons cornstarch", "3 tablespoons vegetable oil", "4 ounces shiitake mushrooms chopped", "1/2 cup red pepper chopped", "2 scallions chopped", "2 cloves garlic minced", "1 tablespoon fresh ginger grated", "1 pound ground chicken", "8 ounces water chestnuts drained, minced", "1 tablespoon cilantro leaves chopped fresh", "1 head Boston lettuce separated into individual leaves for \"cups\""""