Preheat oven to 400 degrees.
Place the spaghetti squash, cut sides up, on a sheet pan. Brush the flesh completely with olive oil and pour the apple cider into the cavities. Sprinkle with 2 teaspoons salt and 1 teaspoon pepper and roast 50 to 75 minutes, until the insides of squash are very tender and shred easily when raked with a fork (squash should be the consistency of al dente pasta). Remove from oven and set aside until cool enough to handle. Shred as much of the squash as possible and transfer it to a large bowl. Discard the shells.
Heat 2 tablespoons of olive oil and the butter in a large sauté pan over medium heat until the butter starts to sizzle. Add the garlic and cook for 1 minute, until fragrant. Immediately add shredded squash and sauté over medium heat, stirring occasionally, for 5 minutes, until heated through. Remove from heat, stir in the Parmesan, parsley, 2 teaspoons salt and 3/4 teaspoon pepper. Taste for seasonings and serve hot.