Place the boneless skinless chicken breasts at the bottom of the crock pot.
Add the diced onion, diced carrots, diced celery, and minced garlic on top of the chicken.
Rinse the quinoa thoroughly under cold water using a fine mesh strainer, then add it to the crock pot.
Pour in the 6 cups of low-sodium chicken broth.
Add the dried thyme, dried oregano, ground black pepper, and salt to the crock pot.
Drizzle the tablespoon of olive oil over the ingredients.
Cover the crock pot and cook on low for 6 hours, or until the chicken is cooked through and vegetables are tender.
After cooking, remove the chicken breasts and shred them using two forks.
Return the shredded chicken to the crock pot and stir in the chopped fresh spinach and lemon juice.
Cover and cook on high for an additional 10 minutes until the spinach is wilted.
Stir the soup well before serving.