Heat butter in a large skillet. Saute mushrooms in melted margarine for 5 minutes. Sprinkle with lemon juice; add frozen peas.
In a bowl, combine chicken broth, cream of chicken soup, milk, parsley and nutmeg. Set aside.
Cook spaghetti according to package directions. Drain.
Pour 2 cups of chicken soup mixture into a lightly greased 9-by-13-inch baking dish. Layer mushroom mixture, spaghetti and turkey over sauce. Pour remainder of sauce over turkey. Sprinkle with Parmesan cheese.
Bake at 350 degrees for 35 minutes.