For marinade, in a medium mixing bowl combine fajita mix, water, and oil. Add chicken to marinade. Stir to coat. Let stand at room temperature for 15 minutes.
Spray a large skillet with nonstick coating. Preheat over medium heat. Add sweet pepper, zucchini, and onion; cook and stir for 2 to 3 minutes or until crisp-tender. Remove from skillet.
Drain chicken; discard marinade. Add chicken to skillet. (If necessary, add 1 tablespoon cooking oil during cooking.) Cook and stir for 4 to 5 minutes or until no pink remains. Return vegetables to skillet. Stir together salsa and chili powder. Add salsa mixture, corn, and beans to skillet. Cook and stir for 1 to 2 minutes more or until heated through. Serve with warm tortillas and cheese, if desired. (To heat tortillas, wrap in microwave-safe paper towels; micro-cook on high power for 30 seconds). Makes 4 servings.