Preheat oven to 400 degrees. Line baking pan with parchment paper.
Slice each squash in half and remove seeds.
Drizzle the open side of each squash with avocado oil. Place open side down and roast for 30 minutes until fork tender.
In a medium skillet, over medium heat, add oil, onion, celery, salt, pepper and sage. Sauté until onions become translucent, approximately 10 minutes.
Add sausage and sauté until fully cooked.
Add apple and sauté until softened.
Remove from heat. Add breadcrumbs and parmesan.
Once Squash has finished roasting (when you can easily poke it with a fork) remove from oven and fill each with prepared stuffing mixture.
Return to oven and roast for 15 minutes until the stuffing is a golden-brown color.
Garnish with additional herbs or parmigiano reggiano if desired and serve!