In a large pot, heat the olive oil over medium heat. Add the diced onion and sauté for about 3-4 minutes until translucent.
Stir in the minced garlic, diced carrots, and celery. Cook for an additional 5 minutes until the vegetables are tender.
Add the dried oregano and thyme, stirring to combine.
Pour in the chicken broth and bring the mixture to a boil.
Add the chicken breasts to the pot. Reduce the heat and let it simmer for about 15-20 minutes, or until the chicken is cooked through.
Remove the chicken from the pot and shred it using two forks. Return the shredded chicken to the soup.
Stir in the uncooked orzo pasta and cook for an additional 8-10 minutes, or until the pasta is al dente.
Add the chopped spinach and lemon juice, stirring well. Season with salt and pepper to taste.
Serve hot, garnished with fresh parsley.