In a bowl, combine cornstarch, garlic powder and lemon zest. Stir in broth and lemon juice until smooth; set aside. In a 3-cup microwave-safe dish, cook pepper and zucchini in butter until crisp-tender. Stir in broth mixture and rice. Cover; microwave on high for 4 minutes. Stir in chicken. Cover and let stand for 5 minutes; fluff rice. Cook 30-45 seconds, until heated through.