Preheat oven to 350°.
Steam cauliflower, covered, 4 minutes or until crisp-tender, and drain. Combine steamed cauliflower, 1 tablespoon cheese, 1/4 teaspoon salt, and 1/8 teaspoon pepper in a 2-quart casserole coated with cooking spray, and toss gently.
Place pumpkin in a food processor, and process until smooth. Add 1/4 teaspoon salt, 1/8 teaspoon pepper, and sour cream, and pulse until smooth. Spoon the pumpkin mixture over cauliflower. Combine 1 tablespoon cheese, breadcrumbs, and parsley; sprinkle over pumpkin mixture. Bake at 350° for 15 minutes.