Preheat oven to 350°. Drain spinach well, pressing between paper towels.
Melt butter in a large saucepan over medium-high heat; add chicken and mushrooms, and onion. Sauté 10 minutes or until chicken is done and mushrooms are tender. Remove from heat. Stir in cream cheese, spinach, soup, and remaining ingredients, fold in cheese.
Spoon 1/4 of chicken mixture in a lightly greased 8- x 8-inch baking dish. Arrange 2 noodles on top of mixture. Repeat layers twice; top with remaining chicken mixture. Sprinkle with Parmesan cheese.
Bake, covered, at 350° for 45 minutes; uncover and bake 15 minutes or until bubbly.