Heat oil in a medium saucepan over medium heat. Add onion, garlic, and red-pepper flakes and cook until tender, 6 to 8 minutes. Add roasted peppers and stock. Bring to a boil; reduce heat and simmer, 10 minutes. Let cool slightly, then puree in a blender until smooth. Season with salt.
In a small bowl, mix together quinoa, red onion, avocado, and cilantro. Season with salt. To serve, ladle soup into bowls, top with quinoa salsa, and squeeze with lime.
The photograph is confusing. There is no spinach or shrimp in the recipe.