Roast: Halve and seed the squash, brush with oil, season, and roast cut side down at 400°F (200°C) for 30 to 35 minutes.
Brown: Cook the sausage in oil until browned, 5 to 6 minutes. Add onion and celery for 4 minutes, then garlic and herbs for 30 seconds.
Mix: Stir in the quinoa, spinach, cranberries, and pecans until the spinach wilts. Off the heat, add half the Parmesan.
Fill and bake: Turn the squash cut side up, fill generously, top with the remaining Parmesan, and bake 12 to 15 minutes until golden.