Preheat oven to 350°F. In a large pot cook pasta according to package directions. Drain cooked pasta, then return to pot.
While the pasta is boiling, make the cheese sauce. In a medium saucepan over medium heat melt butter. Stir in flour, salt, and pepper. Add whipping cream and milk stirring until slightly thickened and bubbly. Add cheese, pumpkin, and sage stir until cheese is melted. Pour over pasta and stir to coat. Transfer to an ungreased 2-quart baking dish.
In a small bowl combine bread crumbs, Parmesan, walnuts, and oil; sprinkle over pasta. Bake, uncovered, for 30 minutes or until bubbly and top is golden. Let stand 10 minutes before serving.