Preheat your oven to 400 degrees and line a baking sheet with parchment paper.
Slice both butternut squash in half lengthwise and cut off the stem and base of the squash.
Using a spoon, scoop out the stringy guts and seeds and brush the cut side of the squash with ½ tablespoon of olive oil.
Place the butternut squash halves cut side down onto your baking sheet and bake uncovered for 45-60 minutes. The squash should be firm but soft, if you prefer a softer squash you can leave it in the oven for 10-minute increments until the desired softness is reached.
While the squash is baking, in a large skillet sauté celery and onion with the remaining ½ tablespoon of olive oil over medium heat until onion is translucent and celery is soft.
In the same skillet with the celery and onion, prepare the stuffing mix in accordance with the package directions however, replace the water with chicken broth. Once done, set aside.
In a medium skillet, brown the Italian sausage and drain any grease it produces.
Combine the sausage with the stuffing until well mixed.
Once your butternut squash is cooked, scoop out a small channel of squash the length of the squash and stuff it with your sausage stuffing mixture.
Top the sausage stuffing butternut squash with parmesan cheese and parsley. Serve warm.