Preheat the oven to 400 degrees.

Slice the two spaghetti squash in half lengthwise (stem to tail) and scoop out seeds and stringy flesh.

Place squash on a rimmed baking sheet and drizzle with 1 of the tablespoons of oil. Sprinkle with salt and pepper then bake for 40 minutes (smaller squash may need only 30-35 minutes).

Meanwhile, in a large skillet over medium heat sauté the chopped onion in the other half of the olive oil (1 tablespoon). Cook the onion until translucent (about 5 minutes). Then, add in the sausage and continue to cook until sausage is all browned. Add in marinara sauce. Once the sauce is hot and bubbling stern in the spinach a handful at a time, until it is all wilted (this should only take a minute or two). If squash is still cooking at this point, remove the skillet from the heat and let sit until squash is ready.

Once squash is out of the oven, use a fork to gently pull the squash flesh from the peel, separating the flesh into strands. If the squash seems too hard to scrape, return it to the oven for an additional 10 minutes. Rake your fork in the same direction as the strands to make the longest "noodles."

Toss the squash noodles into the sauce mixture then place back into the peels.

Topp each squash half with cheese, dividing the mozzarella and parmesan between the 4 halves.

Place back in the oven for 15 minutes or until cheese is bubbly.