1. In a small bowl, stir together broth, soy sauce, sherry, oyster sauce, and cornstarch. Set sauce aside.
2. In a wok or large frying pan, heat oil over medium-high heat. Add chicken and stir-fry 2 minutes. Add zucchini, garlic, jalapeno, and 1/2 cup of scallions. Stir-fry 1 minute. Stir sauce to blend cornstarch, add, and cook, stirring, until thickened, about 2 minutes.
3. Serve spooned over chow mein noodles. Sprinkle remaining scallions on top.