Preheat oven to 400°F. Halve the spaghetti squash lengthwise, brush the cut sides with olive oil, and season with salt. Place cut-side down on a parchment-lined baking sheet. Roast for 40 to 45 minutes, until a fork pierces the skin easily.
While the squash roasts, heat 2 tablespoons of olive oil in a large skillet over medium heat. Add the carrots, onion, and celery; cook, stirring occasionally, for about 8 minutes until softened and slightly golden.
Add the garlic and cook for 30 seconds. Add the ground turkey and break it up with a wooden spoon, cooking until no pink remains, about 6 to 8 minutes.
Stir in the mushrooms and cook until they release their liquid and reduce, about 4 minutes. Add the tomato paste and stir to coat everything, cooking for 2 more minutes.
Add the crushed tomatoes, oregano, salt, and pepper. Stir well, reduce heat to low, and simmer uncovered for at least 20 minutes, until thickened and flavorful.
When the squash is done, let it cool for 10 minutes. Use a fork to scrape the strands into a colander or onto a clean kitchen towel. Press out as much moisture as possible.
Portion into five glass meal prep containers: squash as the base, bolognese ladled on top. Add a pinch of Parmesan if packing now, or store cheese separately. Let containers cool fully before sealing.
Label each container with the prep date and refrigerate.