1. Using a sharp knife, trim off the very top and bottom of each squash to create a flat base on each side.
2. Slice the squash in half, scrape out seeds to create individual bowls for the stuffing.
3. Drizzle each squash half with olive oil, salt, and pepper.
4. Roast in a preheated oven at 400°F (200°C) for 40-50 minutes - or until fork tender.
5. While squash is roasting - in a large frying pan over medium heat - heat oil and add onion, salt, pepper and rosemary. Cook until onions begin to soften.
6. Add garlic and sausage, until sausage is browned on all sides.
7. Finally, mix in bread crumbs and Parmesan cheese just until incorporated. Remove from heat.
8. Once squash has finished roasting (when you can easily poke it with a fork), remove from oven and fill each with prepared stuffing mixture.
9. Return to oven for 20 minutes, adding a sprinkle of Parmesan cheese to the top for the final 5 minutes. Enjoy!