Place the chicken breasts, onion, carrots, celery, garlic, chicken broth, Italian seasoning, salt, pepper, and thyme into your crock pot.
Cover and cook on LOW for 5–6 hours or HIGH for 3 hours, or until the chicken is cooked through and tender.
Remove the chicken from the crock pot and shred it with two forks. Return the shredded chicken to the soup.
Stir in the orzo. Cover and cook on HIGH for about 20–30 minutes, stirring once or twice, until the orzo is tender.
Stir in the fresh spinach and allow it to wilt for 2–3 minutes.
Squeeze the juice of one lemon into the soup. Taste and add more lemon juice if you'd like a stronger lemon flavor.
Stir in the fresh parsley and serve warm with an extra squeeze of lemon, if desired.