Heat the olive oil in a large pot or Dutch oven over medium heat. Add the diced onion, carrots, and celery (the mirepoix). Sauté for 6-8 minutes, until the vegetables have softened.

Add the minced garlic, dried oregano, and dried thyme to the pot. Cook for another minute until fragrant, stirring constantly to prevent the garlic from burning.

Pour in the chicken broth and add the whole chicken breasts to the pot. Season with salt and pepper. Bring the soup to a boil, then reduce the heat to a simmer. Cover and cook for 15-20 minutes, or until the chicken is cooked through and no longer pink inside.

Carefully remove the cooked chicken breasts from the pot and place them on a cutting board. Once cool enough to handle, use two forks to shred the chicken into bite-sized pieces. Set aside.

Bring the broth back to a gentle boil. Stir in the uncooked orzo pasta. Cook according to package directions, typically 8-10 minutes, until the orzo is al dente. Stir occasionally to prevent it from sticking to the bottom of the pot.

Turn off the heat. Stir the shredded chicken back into the soup. Add the fresh lemon juice, lemon zest, and chopped fresh dill (or parsley). Stir to combine.

Taste the soup and adjust seasoning with more salt, pepper, or lemon juice if needed. Serve hot and enjoy.