In a large pot or Dutch oven, heat the olive oil over medium heat. Add the chopped onion, carrots, and celery, sautéing until the vegetables are softened, about 5-7 minutes.
Stir in the minced garlic and cook for an additional minute until fragrant.
Add the chicken breasts to the pot, followed by the chicken broth, lemon juice, and lemon zest. Season with oregano, salt, and pepper. Bring to a boil.
Reduce the heat to a simmer and cover the pot. Cook for 15-20 minutes, or until the chicken is fully cooked and tender.
Once the chicken is cooked, remove it from the pot and shred it with two forks. Return the shredded chicken to the pot.
Add the orzo to the soup and cook for an additional 8-10 minutes, or until the orzo is al dente.
Stir in the chopped spinach and let it wilt for a couple of minutes.
Taste and adjust seasoning with more salt, pepper, or lemon juice if desired.
Serve hot, garnished with fresh dill or parsley.
Notes
Adjust seasoning to taste and use fresh herbs for garnish.