Place a 3-quart pot over high heat. Add 1 tablespoon of butter. Once melted add the onion, celery, and carrots to the pot and cook for 4-5 minutes until the onion is translucent.
Add the garlic and chicken and cook for another 2-3 minutes, stirring often.
Add 1 tablespoon of butter and once melted, stir in the flour. Cook for 1-2 minutes. Add the herbs, chicken stock, and orzo to the pot, and bring to a boil.
Reduce the heat to medium-low and simmer for 13-15 minutes until the orzo is cooked.1
Stir in half the lemon juice and lemon zest. Check the seasoning and add more salt and pepper to taste. If desired, add in more lemon juice and lemon zest to taste. Serve warm garnished with lemon slices and parsley.
Notes
For even more flavor you can use bone-in chicken breast or chicken thighs. Cook them, remove the chicken from the soup, take the meat off the bones and then add the meat back to the soup.