Roast the spaghetti squash and set aside until cool enough to handle. Use a fork to pull the flesh apart and away from the sides. The flesh will form "spaghetti-like" noodles as it separates.
While the squash cools, melt 4 tablespoons of butter in a large skillet over medium heat. Add the garlic and cook, stirring frequently, until fragrant, about 1-2 minutes.
Add the remaining ¼ cup of butter and allow it to melt. Add the spaghetti squash to the butter mixture and gently toss to combine.
Add the Parmesan and parsley and toss again to mix throughout. Season with salt, taste, and adjust salt, as desired. Serve immediately, topped with additional Parmesan and parsley, if desired.