Preheat oven to 400°F (200°C). Place squash cut side up on a baking sheet. Drizzle with oil, season with salt and pepper. Roast for 35-40 minutes until tender.
Meanwhile, in a skillet, cook sausage until browned. Add onion and garlic; cook until softened. Stir in thyme, red pepper flakes, and rice. Mix and remove from heat.
Optional: Scoop a bit of cooked squash flesh and mix it into the filling. Stir in Parmesan, breadcrumbs, and parsley.
Lower oven to 375°F. Fill each squash half with stuffing. Bake 15-20 minutes more, until tops are golden.
Notes
Try adding chopped nuts or dried cranberries for extra texture. Vegetarian sausage works great too!