Preheat the oven to 400°F (200°C). Cut the spaghetti squash in half lengthwise and scoop out the seeds. Drizzle with olive oil, and sprinkle with salt and pepper. Place cut-side down on a baking sheet lined with parchment paper. Roast for 25-30 minutes or until the flesh is tender and can be easily shredded with a fork.
While the squash is roasting, heat a large skillet over medium heat. Add the chicken sausage, breaking it apart with a spatula. Cook until browned and cooked through, about 5-7 minutes.
Add the diced onion and sauté for 3-4 minutes until translucent. Stir in the minced garlic and diced red bell pepper, cooking for another 3 minutes until softened.
Add the chopped kale (or spinach) to the skillet and cook until wilted, about 2 minutes. Stir in the cherry tomatoes, dried oregano, and red pepper flakes, cooking everything together for an additional 2-3 minutes. Season with salt and pepper to taste.
Once the spaghetti squash is cooked, carefully shred the flesh with a fork to create noodles. Combine the squash strands with the sautéed sausage and vegetables in the skillet, tossing everything together.
Remove from heat and stir in half of the grated Parmesan cheese until melted and evenly distributed.
Serve hot, divided among bowls, and garnish with the remaining Parmesan cheese and fresh basil leaves.
Notes
Feel free to substitute kale with spinach if preferred.