Preheat oven to 400°F. Line a baking sheet with parchment paper. Cut a thin slice from each end of squash to stabilize. Cut into two equal halves through the middle or from top to bottom.
Use a spoon to scoop out seeds. Season each half with salt pepper and drizzle with oil. Place seam side down on pan. Bake for 40 minutes.
Meanwhile to make the filling: In a large skillet melt butter over medium high heat. Add onion, celery, salt, pepper, rosemary and thyme. Cool for 3 minutes until beginning to soften.
To the skillet, add sausage and garlic. Continue to cook over medium high until no pink remains. Add, apple cooking until softened about 2-3 minutes.
Remove from heat adding bread crumbs and 1 tablespoon parsley. Mix well.
Remove squash from oven and flip over. Divide filling among acorn halves and sprinkle the tops with shredded Parmesan cheese.
Return to the oven baking for an additional 15-20 minutes or until squash is easily pierced with the tip of a knife. Sprinkle the tops with shredded Parmesan cheese in the last 5 minutes of baking.
Serve immediately garnished with reserved parsley.