Begin by heating the olive oil in a large cast-iron pot or skillet over medium-high heat. You’ll know it’s ready when the oil shimmers. This step is crucial as it sets the base for all the flavors to develop.
Once the oil is hot, add the diced onion, diced carrots, and diced celery. Stir these together and let them cook for about 7 to 9 minutes until they’re tender. The onion should become translucent, and the mixture will start to smell fantastic.
Next, add in the minced garlic, tomato paste, Italian seasoning, dried oregano, dried basil, dried thyme, and red pepper flakes, if you’re using them. Season with salt and pepper to taste. Stir everything well for about 1 to 3 minutes until it’s fragrant.
After that, transfer this aromatic mixture to a 6-quart slow cooker. Make sure to scrape the bottom of the pot to get all the delicious bits into the slow cooker.
For the chicken, remove any visible fat from the boneless, skinless chicken breasts. Cut each breast into chunks, about 3 to 5 pieces each. This ensures even cooking. Place the chicken into the slow cooker.
Now, add the undrained fire-roasted diced tomatoes, uncooked quinoa, bay leaves, and chicken stock into the slow cooker. Stir everything together until evenly mixed.
Cover the slow cooker and set it to high. Let the soup cook for about 3 to 5 hours. You’ll know it’s done when the quinoa has “popped” and the chicken shreds easily. I recommend against cooking on low, as it changes the texture of the quinoa.
Once the chicken is tender, carefully remove it from the slow cooker into a bowl. Using two forks, shred the chicken into bite-sized pieces and return it to the soup.
Remove the bay leaves and discard them. If you want to add some greens, now’s the time to stir in the coarsely chopped baby spinach and let it wilt in the warm soup.
Finally, taste your Chicken Quinoa Soup and adjust the seasoning with additional salt and pepper as needed. Ladle the soup into bowls, and if you wish, garnish with fresh basil and a generous sprinkle of freshly grated Parmesan cheese. Serve with warm, hearty bread on the side.
