Preheat oven to 425°F.
Place spaghetti squash cut-side up on a baking sheet. Spray with olive oil cooking spray to coat the top and season with salt and pepper. Bake until brown on top and soft all over, about 30-35 minutes. Remove from oven and let cool while meatballs bake.
Lower oven temp to 375°F.
In a food processor, pulse rolled oats for a few seconds until they are ground but not powdery.
In a mixing bowl, combine oats and milk until well-combined. Add turkey, egg, garlic, cheese, spinach or kale, chili flakes, oregano, salt and pepper. Using your hands, combine mixture well, making sure not to overmix.
Coat a large baking sheet with olive oil spray. Using a 1 1/2- to 2-inch kitchen scoop, scoop meat mixture onto the baking sheet. Roll the meatballs into balls with your hands then spray the tops of the meatballs with olive oil cooking spray. Bake in the oven for 12-14 minutes or until brown on top and cooked through.
For the tomato sauce, heat olive oil in a large saucepan over medium-high heat. Add onion, garlic and bay leaf, and sauté 3-4 minutes. Add tomato paste and cook for another minute. Deglaze pan with red wine, and reduce the wine by half. Add crushed tomatoes and bring to a bubble. Reduce heat to simmer and cook for 18-20 minutes. Remove bay leaf and stir in basil.
To serve, scrape spaghetti squash into a serving bowl. Top with meatballs and tomato sauce.