In a saucepan over medium-high heat, add 2 tablespoons of the grapeseed oil, the celery, onion, garlic, and peppers. Stir while cooking until the onions are translucent, about 12 minutes.
In a separate saucepan, over medium heat add the remaining 1 tablespoon of oil, the tomato juice, canned tomatoes, oregano, chicken, basil, and broth and simmer for 10 minutes. Add the vegetable mixture and stir to combine. Continue to cook over medium heat for 10 minutes, then reduce the heat to low, and cook for another 10 minutes, stirring throughout the cooking time.
Once the sauce has reduced, add the pasta and the green onions. Stir in the Parmesan and transfer the spaghetti to a serving bowl.