2 ounces cream cheese
2 medium spaghetti squash (about 5 pounds total)
1 tablespoon olive oil
3/4 teaspoon kosher salt
1/4 teaspoon freshly ground black pepper
3 ounces whole-milk, low-moisture mozzarella cheese, shredded (about 3/4 cup)
2 ounces Parmesan cheese, grated (about 1 cup), divided
2 tablespoons chopped fresh parsley leaves, plus more for garnish
1/2 teaspoon garlic powder
Arrange a rack in the middle of the oven and heat the oven to 400°F. Line a rimmed baking sheet with aluminum foil or parchment paper; set aside. Place 2 ounces cream cheese in a large bowl and let sit out at room temperature while the oven heats to soften.
Cut 2 spaghetti squash in half lengthwise and scoop out the seeds. Brush the cut sides of the squash with 1 tablespoon olive oil and season with 3/4 teaspoon kosher salt and 1/4 teaspoon ground black pepper. Arrange the squash cut-side down on the baking sheet. Roast until the squash are soft when poked with a fork and the skin is browned and blistered, about 40 minutes.
Shred 3 ounces mozzarella cheese (about 3/4 cup) and grate 2 ounces Parmesan cheese (1 cup). Chop until you have 2 tablespoons fresh parsley leaves, plus chop a little extra for garnish. Add the mozzarella, 3/4 cup of the Parmesan (set aside the remaining 1/4 cup for topping), 2 tablespoons parsley, and 1/2 teaspoon garlic powder to the cream cheese and stir with a rubber spatula to combine.
Remove the baking sheet from the oven. Flip the squash over and use a fork to shred the inside of each squash half, leaving about 1/2-inch of unshredded squash left in the shell. Transfer the shredded squash to the cream cheese mixture and toss to combine. Evenly divide the filling between the squash halves, then sprinkle with the remaining 1/4 cup Parmesan.
Bake until the cheese is melted, 8 to 10 minutes. Turn the oven on to broil and broil until browned and bubbly, 2 to 3 minutes more. Garnish with more parsley and serve hot.
Make ahead: The squash can be roasted and shredded a day in advance and refrigerated in an airtight container. Add an extra 10 minutes to the baking time.
Storage: Refrigerate leftovers in an airtight container for up to 4 days.