Pre-heat oven to 400 degrees.
Cut acorn squash in half. Remove seeds. Brush with olive oil. Season with salt and pepper to taste.
Bake acorn squash face up for 1 hour.
While acorn squash is baking, cook the sausage until there is no pink. Also, break up sausage so it is in small crumbles. Once cooked, add the onion and celery. Cook for an additional 5 minutes or until the onion becomes fragrant and translucent.
Add apples pieces and cook for another 2 minutes until apples are softened.
Add the Rosemary and 3/4 cup of the shredded Parmesan cheese. Cook until the cheese is melted.
Once squash has finished baking, remove from oven and fill with sausage mixture. Sprinkle with breads crumbs and remaining Parmesan cheese. Drizzle melted butter over the top. Bake for another 15-20 minutes.
Keto Friendly: don't add bread crumbs! And you have a Keto friendly meal!
Be careful removing the acorn squash half's from the pan! They will be extremely hot and a little soft! I used two forks poked into either side to lift and place on a plate! Then enjoy!