Place the squash face down in a baking dish with ½ cup water for 30-45 minutes until fork tender.
While the squash is cooking, slice the sausage into ½ inch chunks and saute in large skillet until browned and cooked through.
Remove the sausage from the pan and set aside.
Dice the onion, bell pepper, and mushrooms.
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 open side is up.
Stuff the squash with the sausage mixture and top with Parmesan if using and put it back into the oven for around 10 minutes to brown.
Remove from oven, cut each squash half in half, serve, and enjoy!
Notes
This is one of those endlessly versatile recipes; choose the type of squash you like, your favorite type of sausage or even leftover chicken, and customize the spices to your tastes!