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 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 ajar), 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. I keep the lid off and stir it fairly often because 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 (you may want to add more than I suggest - I didn't want to make the soup too lemony for some people), parsley, and season the soup with salt & pepper as needed. Serve immediately.
You can sub the chicken breasts for chicken thighs if you prefer.
Chicken is safe to eat at 165F and can go from undercooked to overcooked quickly, so I recommend using an instant read meat thermometer whenever cooking chicken so you're not guessing.
Use low-sodium chicken broth if you're sensitive to salt.
You may need to add more chicken broth to leftovers as the orzo soaks it up.
Nutritional information is provided as a courtesy only and should be construed as an estimate rather than a guarantee. Ingredients can vary and Salt & Lavender makes no guarantees to the accuracy of this information.