Preheat oven to 350 degrees Fahrenheit. Cook the pasta according to package instructions. Drain and return to the pot.
In a medium pan, melt the butter over low heat. Whisk in the flour, salt, pepper. Add the cream and milk, whisking constantly. Increase the heat to medium and stir until the sauce begins to thicken and bubble around the edges.
Add the pumpkin and cheese to the cream sauce. Whisk to blend. Add pasta to sauce and stir until well coated. Stir in greens. Transfer pasta mixture to a 9 x 9 inch (1.5 quart) baking dish.
In a small bowl, combine the breadcrumbs and Parmesan cheese; sprinkle over pasta. Bake uncovered for 30 minutes or until the breadcrumbs are golden brown and cheese is bubbly. Let stand 10 minutes before serving.