Preheat the oven to 400°F.
Cut the spaghetti squash in half lengthwise and scoop out the seeds.
Drizzle the inside with 1 tablespoon of olive oil and sprinkle with salt and pepper.
Place cut-side down on a baking sheet and roast for 30-40 minutes, or until tender.
In a large skillet, heat the remaining tablespoon of olive oil over medium heat.
Add the diced chicken, garlic, Italian seasoning, salt, and pepper. Cook for about 5-7 minutes, or until the chicken is cooked through.
Add the chopped spinach and cook until wilted, about 2-3 minutes.
In a large bowl, combine the cooked chicken and spinach mixture with the cream cheese and half of the Parmesan cheese. Mix until well combined.
Once the spaghetti squash is done, let it cool slightly. Use a fork to scrape the flesh into strands and add it to the chicken mixture. Stir until everything is well combined.
Spoon the mixture back into the spaghetti squash halves. Top with the remaining Parmesan cheese and mozzarella cheese.
Return to the oven and bake for an additional 10-15 minutes, or until the cheese is melted and bubbly.
Serve warm, garnished with fresh parsley if desired.