Cook cauliflower in boiling water 4 minutes or until tender; strain. Mix together cauliflower, Parmesan, 1/4 teaspoon salt, and 1/8 teaspoon pepper in a cooking spray coated casserole dish.
Using a food processor or blender, puree pumpkin until smooth. Mix in 1/4 teaspoon salt, 1/8 teaspoon pepper, and sour cream. Spread pumpkin mixture over cauliflower and top with cheese, breadcrumbs, and parsley. Bake 15 minutes.