In same skillet, heat remaining 1 tablespoon oil. Add onion and zucchini; cook about 6 minutes, stirring frequently, until zucchini is crisp-tender. Return chicken to skillet (discard chicken juices). Stir in garlic, chili powder, oregano and salt. Cook 2 minutes, stirring constantly. Stir in tomatoes; cook until thoroughly heated. Remove from heat.