Sauté the celery, carrots, and onions in a large soup pot with the butter and oil over medium-high heat for 5-7 minutes.

Stir in the garlic and cook for about 30 seconds, then add the flour and cook for another minute or so.

Pour in the chicken broth and stir until the flour has dissolved, then add the Italian seasoning and chicken. Bring the soup to a boil.

Cover the soup (lid slightly open), and reduce the heat and simmer for 15 minutes.

Stir in the orzo and cook for another 10 minutes or until the orzo is cooked through. Keep the lid off and stir it fairly often as it tends to stick to the bottom of the pot.

Take the chicken out of the pot and cut it up, then add it back in. Add the lemon juice, parsley, and season the soup with salt & pepper as needed. Serve immediately.