Heat oil in a large skillet over medium-high heat. Add chicken and stir-fry for 6 minutes; remove to a plate.
Add mushrooms, sweet red pepper, scallions, garlic, five-spice powder and red pepper flakes. Stir-fry for 3 minutes or until mushrooms and peppers are tender. Stir in water chestnuts, broth, soy sauce and hoisin sauce. Bring to a simmer; add chicken and cook for 3 minutes, stirring occasionally.
To serve, spoon chicken mixture into lettuce leaves and sprinkle with some rice noodles. If desired, serve with duck sauce for dipping.
