Carefully split the spaghetti squash in half lengthwise.
In a 3 quart casserole dish place a shallow amount of water to the bottom of the dish until the bottom is covered, just.
Place each squash half, open face down on the casserole dish within the shallow water. Bake for 35-45 minutes, or until the squash is just soft and stringy to the touch.
Leaving the oven on, Remove the baked squash from the oven. Carefully start scrapping the squash from the shell (it will be hot), placing the scrapped contents in a medium-large bowl. Be sure to save your shells, simply place the empty shells back in the same shallow casserole dish. These will be reused in a just a bit.
Add the Spaghetti sauce, salt and garlic powder in with the spaghetti squash that was scrapped into the medium bowl and mix until well combined.
Fill the shells. Start will a base layer to each shell with the spaghetti squash, add a light layer of the cubed sausage followed by a light layer of the shredded mozzarella cheese. Repeat this process until all ingredients are evenly layered between both shells. Top with any remaining cheese and add the Parmesan cheese evenly to the top. Place back in the oven and allow to heat through for an additional 10-15 minutes or until bubbly and all the cheese is melted.
Remove from the oven and allow to sit for 3-5 minutes. Plate & Serve.