Heat oven to 400°F. Spray 3-quart glass casserole with cooking spray. In 12-inch nonstick skillet, cook chicken over medium heat 8 to 10 minutes, stirring occasionally, until no longer pink. Stir in onion, zucchini, pasta and water. Cook 5 to 6 minutes, stirring occasionally, until vegetables are crisp-tender.
Stir in tomatoes, pasta sauce, cheese and Italian seasoning. Spoon mixture into casserole. Brush top of each of phyllo sheet with melted butter. Crumple each phyllo sheet and place on top of chicken mixture in casserole. (See photo for example on how to cover top of chicken mixture.)
Bake uncovered 20 to 30 minutes or until phyllo is golden brown.