1. In a large slow cooker, combine the onions and olive oil. Stir well to coat, then cover and cook on LOW for 6 to 8 hours, or until well browned and caramelized.
2. When the onions are done, bring a large saucepan of salted water to a boil.
3. Add the pasta and cook according to package directions. Drain, then set pasta aside.
4. In the same pot you used to boil the pasta, add the caramelized onions, creme fraiche, arugula and sun-dried tomatoes. Stir over medium heat until the arugula just begins to wilt and the cream fraiche is heated through.
5. Plate the pasta, spoon the caramelized onion-creme fraiche mixture over it then season with salt, freshly grated black pepper; garnish with fresh parsley.