Cut the squash in half from top to bottom and remove the seeds.
Place the squash cut side down in a baking dish with ½ cup water. Bake for 30-45 minutes until fork tender.
While the squash is cooking, saute the sausage in a large skillet over medium-high heat until browned and cooked through.
Remove the sausage from the pan and set aside.
Add the diced onion, bell pepper, and mushrooms to the pan and cook until almost soft
Remove from the heat and add the sausage back in as well as the butter and spices and mix well.
When the squash is cooked, remove it from the oven and turn it over so the cut side is up.
Stuff the squash with the sausage mixture and top with Parmesan if using. Put the stuffed squash back into the oven for around 10 minutes to brown.
Remove from the oven, cut each squash half in half, serve, and enjoy!
Notes
You can also skip the water while cooking for a roasted squash version. Instead, place the oiled squash cut side down onto a parchment paper lined baking sheet. The squash will be more caramelized this way instead of steamed.