1. To prepare the spaghetti, preheat oven to 400 degrees. Drizzle cut sides of squashes with oil; season with salt and pepper. Place cut sides up on a baking sheet. Bake until soft to the touch, 1 to 1 1/4 hours.

2. To prepare the sauce, heat the oil in a saucepan over medium-high heat. Add the garlic and cook, stirring with a wooden spoon, for 1 minute. Add the tomato paste and cook, stirring, for an additional minute. Stir in the tomatoes and oregano; season with salt and pepper. Bring to a boil, and reduce to a simmer. Cook, stirring occasionally, until thickened, about 20 minutes. Keep warm over low heat.

3. Prepare the meatballs. In a medium bowl, stir together the breadcrumbs, Parmesan, parsley, and garlic with a wooden spoon until combined. Add the milk, and stir until incorporated. Add the turkey, egg, salt, and pepper, and mix with your hands until well combined. Form mixture into 1 1/2-inch balls.

4. Heat the olive oil in a large nonstick skillet over medium-high heat. Working in 2 batches, cook the meatballs until evenly browned, turning often, about 6 minutes. Repeat with remaining meatballs. Transfer meatballs to the sauce, and simmer until cooked through, about 10 minutes.

5. When the squashes are cool enough to handle, scrape the flesh of each squash with a fork into strands, and place into a large bowl. Serve topped with meatballs and sauce, and sprinkled with cheese, if desired.