Preheat oven to 400 degrees F.
Cut spaghetti squash across the width into 4 rings and place on an oven-safe cooling rack set over a baking sheet. Deseed the squash by running a small knife around the seeds, if you like (you can also deseed after roasting in the same manner).
Liberally salt both sides of each squash ring and set aside for at least 15 minutes, allowing time for the salt to draw out some of the water from the squash.
Wipe away the liquid that the salt has drawn away from the squash with a paper towel, then place the baking sheet in the oven for 30 minutes.
While the spaghetti squash being prepared, put a large pot of water on the stove to boil.
Cut the head of cauliflower into equal sized pieces, about 1-2 inches in diameter.
Add the cauliflower and peeled garlic cloves into the boiling water, and cook for 8 minutes.
Strain the cauliflower and garlic out of the water and place in a blender.
Turn the heat of the pot of water down to low until you are ready to cook the pasta (if using).
Add the cashews, miso, nutritional yeast, salt, and non-dairy milk to the blender, and puree until smooth and creamy.
If using the pasta, place it in the boiling water to cook for the time directed on the package.
When the squash is done roasting, allow to cook for 5-10 minutes before removing the squash from the skin and cutting away the seeds.
Drain the pasta, if using, and return to the pot, along with the spaghetti squash.
Pour the sauce over the squash and pasta, a little at a time, mixing with tongs or a fork until fully coated, adding more sauce as needed. Refrigerate any leftover sauce for another use.
Add optional toppings, and serve.