Bring water to a boil in a Dutch oven. Add pasta and vegetables; cook 5 minutes. Drain.
While pasta and vegetables cook, combine 1/2 cup milk and flour; stir well. Combine flour mixture, remaining milk, Italian seasoning, and next 3 ingredients in a medium saucepan. Cook over medium heat, stirring constantly, until thickened and bubbly. Stir in 1/2 cup Parmesan cheese.
Combine pasta mixture and cheese sauce; stir well. Spoon into an 11- x 7- x 1 1/2-inch baking dish coated with cooking spray. Sprinkle with breadcrumbs. Bake at 350° for 15 minutes. Sprinkle remaining 1/4 cup cheese over breadcrumbs; bake 5 additional minutes or until lightly browned.