Preheat the oven to 400, line a baking sheet with foil and spray with cooking spray.
Drizzle olive oil over the 2 halves of squash and lightly season with salt and pepper.
Place open side down on the prepared baking sheet and bake until fork tender, about 35-45 minutes.
Remove from the oven and let cool for 15-20 minutes.
Decrease the oven temperature to 350.
In a large saucepan, melt the butter over medium heat. Add the garlic and flour and whisk continuously for 2 minutes. Slowly pour in the milk while whisking. Reduce the heat to medium-low and add the salt and pepper. Bring to a simmer and cook until thickened. Add the parmesan cheese and whisk until melted.
Remove the flesh of the spaghetti squash and use a fork to help separate them into strands. Add the squash to the sauce along with the shredded chicken and toss to combine. Add the mixture back into the shells of the spaghetti squash, top with the mozzarella cheese, and place back on the baking sheet. Bake for about 10 minutes, and then turn the broiler on high. Watch carefully, and only broil until the cheese is melted and a few spots are brown, about 90 seconds.
Remove from the oven and garnish with parsley, if desired.
Notes
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