Heat the olive oil in a large pot over medium-high heat. Add the onion, celery, carrots and Cajun seasoning and cook, stirring occasionally, until the vegetables are slightly soft, about 4 minutes.
Stir in the quinoa, then add the chicken broth, 3 cups water, 1/2 teaspoon salt, and pepper to taste. Partially cover and bring to a simmer, then reduce the heat to medium and cook until the quinoa starts to soften, about 12 minutes. Add the broccoli and cook, uncovered, until just tender, about 5 minutes. Add the chicken and stir to warm through. Season with salt and pepper.
Ladle the soup into bowls. Top with the sour cream and Cajun seasoning to taste.
Notes
Can I use any kind of quinoa in chicken quinoa soup? Yes, you can use any quinoa you would like in this soup. Red quinoa, multi-colored quinoa, or white quinoa will work in this soup.
Can I replace quinoa with another grain? We have only tested this soup with quinoa. Feel free to test it with farro, barley, or any other grain and let us know how it works!
What other vegetables can I put in chicken quinoa soup? This chicken quinoa soup has classic vegetables like carrots, celery, and onion. If you would like to add other vegetables to this soup, feel free.
How long can I keep chicken quinoa soup in the refrigerator? Store this soup in an airtight container for 5-7 days in the refrigerator.
Can I freeze chicken quinoa soup? Yes, you can freeze this soup. Let the soup cool completely before placing it into a freezer-safe container. Freeze the soup for up to 3 months.