Using a dish towel, gently wipe mushrooms clean and slice.
Preheat oven to 350 degrees. Lightly grease a 9 x 9-inch baking dish.
Cook pasta in a large pot of boiling water according to package directions.
In a large saucepan over medium heat, melt the butter and stir in flour. Cook and stir constantly for about 2 minutes.
Whisk in the milk and chicken broth a little at a time and bring it to a boil.
Stir in mushrooms and reduce the heat. Cook and stir frequently for about 10 minutes or until the mixture thickens and the mushrooms are softened.
Stir in Parmesan cheese, pasta, turkey and peas into the milk mixture. Spoon into lightly greased dish.
Sprinkle grated cheddar cheese on top. Cover loosely with foil. Bake for about 45 minutes or until it is bubbling at the edges and heated through. Season with pepper if desired.