Preheat the oven to 375°F.

Cut the spaghetti squash in half lengthwise, scoop out the seeds and sprinkle with salt.

Place the squash, cut side down in a baking dish and add about 1/4 inch of water.

Tent with foil and bake until the squash is tender when pierced with a sharp knife, about 45 to 50 minutes.

Remove from the oven and use a fork to rake the strands of flesh out of the skin and into a bowl. Set aside.

Heat the olive oil and butter in a large skillet over medium heat. Add the onion and sauté until soft and lightly caramelized, 5 to 7 minutes.

Add the garlic and continue to sauté for 2 to 3 minutes longer.

Add the spaghetti squash and toss to combine thoroughly. Season to taste with salt and pepper and cook for 2 to 3 minutes to be sure the squash is heated through.

Add the parsley and Parmesan and toss again.