Coat a large skillet with cooking spray; cook and stir chicken and onion over medium heat for 6-8 minutes or until chicken juices run clear. Remove from the heat; stir in spinach.
In a large bowl, combine the soup, milk, sour cream and seasonings. Stir 3/4 cup soup mixture into chicken mixture. Place filling down the center of each tortilla. Roll up and place, seam side down, in a 13x9-in. baking pan that has been sprayed with cooking spray. Pour the remaining soup mixture over enchiladas.
Cover and bake at 350° for 30 minutes. Uncover and sprinkle with cheese; bake 15 minutes longer or until cheese is melted and bubbly. Garnish with parsley.