Preheat your oven to 400°F (200°C).

Cut the spaghetti squash in half lengthwise and scoop out the seeds. Drizzle the insides with olive oil, then sprinkle with salt and pepper. Place cut-side down on a lined baking sheet.

Roast the squash for about 40-45 minutes, or until tender and can be scraped into strands.

In a mixing bowl, combine ricotta cheese, half of the mozzarella, ground turkey (if using), Italian seasoning, salt, and pepper.

Once the squash is cooked, let it cool for a few minutes, then scrape out the flesh into strands and add to the ricotta mixture. Combine until evenly mixed.

In a greased baking dish, spread half of the marinara sauce on the bottom, layer the spaghetti squash mixture on top, followed by the remaining sauce. Finish with the rest of the mozzarella and sprinkle with Parmesan cheese.

Combine breadcrumbs with olive oil, sprinkle over the top layer, and bake for an additional 20-25 minutes until cheese is bubbly and top is golden brown.