Rinse the quinoa to remove any bitter resin. Heat a medium saucepan over medium-high heat. add the remaining olive oil the pan and swirl to coat. Add the onion to the pan and saute until tender, about 5 minutes. Add the quinoa and cook for two minutes, stirring constantly. Add the broth, scraping up any browned bits, and bring to a boil. Cover, reduce the heat, and simmer for 15 minutes or until the liquid is absorbed. Remove the pan from the heat. Stir in the walnuts and season to taste with salt and black pepper.