In a large saucepan, melt the margarine; add sliced mushrooms and cook until tender, about five minutes. Stir in flour; blend well. Add milk. Cook over medium heat until mixture thickens and boils, stirring constantly. Stir in 1/3 cup parsley. Heat over to 325 degrees. To assemble, spread 1/2 cup sauce in ungreased 9 x 13" baking dish. Layer 1/3 of noodles, 1/3 of Ricotta cheese, 1/3 of Mozzarella, 1/3 of remaining sauce, and 1/3 of Mozzarella, 1/3 remaining sauce, and 1/3 Parmesan cheese. Repeat layers ending with Parmesan cheese on top. Bake at 325 degrees for 45 minutes or until bubbly. Let stand 10 - 15 minutes. ENJOY!