Cook spaghetti in boiling salted water until done. Drain and rinse with hot water. Preheat the oven to 350°F. In a large skillet, brown the ground beef with the onion drain. Stir in the tomato sauce, Italian seasoning, and drained mushrooms. Simmer for 10-15 minutes to blend the flavors.
Combine the cooked spaghetti, beaten eggs, ¼ cup Parmesan cheese and the garlic salt. Press the spaghetti mixture onto the bottom and up the sides of a greased 10-inch pie pan to form a crust. Pour the meat mixture over the crust and sprinkle with the remaining Parmesan cheese. Bake at 350°F. for 25-30 minutes or until the crust is set and the edge is slightly browned. Let stand for five minutes before serving. Serves 6.