1. Mix soy sauce, broth, sesame oil, and cornstarch in a 2-cup measure.
2. Place chicken breasts in a food processor. Drizzle the marinade over the top and process mixture until the chicken is ground, or finely chop it. Spoon mixture into a small bowl, cover, and refrigerate for at least 30 minutes.
3. Heat a nonstick skillet over medium heat. Add canola oil, garlic, and ginger and cook about 10 seconds. Add the chicken mixture, breaking lumps into small pieces with a spatula until chicken is cooked thoroughly, about 6 minutes.
4. Add chopped scallions, carrot, and celery; cook, tossing with the spatula, for 1 minute, or until tender. Stir in hoisin and plum sauces; toss.
5. Spoon chicken mixture into each lettuce leaf and sprinkle with 1 tablespoon of the chow mein noodles; wrap the leaf around to make a pouch.
How kids can help: Measure soy sauce, broth, sesame oil, and cornstarch.