Heat olive oil in a large pot over medium heat.
Add chopped onion, diced carrots, and diced celery to the pot. Sauté for about 5 minutes until vegetables are softened.
Add minced garlic and cook for 1 minute until fragrant.
Pour in the chicken broth and bring to a boil.
Add the whole chicken breasts to the boiling broth. Reduce heat to a simmer and cook for 15 minutes, or until the chicken is cooked through.
Remove the chicken breasts from the pot and set aside to cool slightly.
Add orzo pasta, dried thyme, and dried oregano to the broth. Simmer for 8-10 minutes until the orzo is tender.
While the orzo cooks, shred the chicken breasts into bite-sized pieces using two forks.
Return the shredded chicken to the pot.
Add chopped spinach and cook for 2 minutes until wilted.
Stir in fresh parsley and lemon juice.
Season the soup with salt and freshly ground black pepper to taste.
Remove from heat and serve hot.