Turkey Tetrazzini with Mushrooms

Melt 1/4 cup butter in a heavy saucepan. Stir in flour and cook 1 to 2 minutes, but do not brown. Add broth, sherry, cream, and oregano. Cook, stirring constantly, until sauce comes to a boil. Add 1/4 cup Parmesan cheese, stirring until melted. Remove from heat and set aside. Melt remaining butter with oil in skillet. Add garlic, scallions, parsley, and mushrooms and saute until mushrooms are brown. Remove from heat. Cook spaghetti according to package directions until al dente. Drain well. Combine sauce, mushrooms, spaghetti, and turkey; season with salt to taste. Pour into greased casserole and sprinkle with remaining cheese. Bake at 375 degrees for 15 minutes, or until bubbly.