1. Heat olive oil in a large pot over medium heat. Add diced onion, carrots, and celery, and cook until vegetables are softened, about 5 minutes.
2. Add minced garlic and cook for an additional minute.
3. Pour in chicken broth and bring to a boil.
4. Add shredded chicken and orzo pasta to the pot. Cook until orzo is tender, about 10 minutes.
5. Stir in lemon juice and dried oregano. Season with salt and pepper to taste.
6. Serve hot, garnished with fresh parsley.