Prep your ingredients and then heat butter over medium-high heat until melted. Add the carrots, onion and celery and sauté until the onions start to become translucent.
Add about 8-9 cups broth, seasoning, garlic, bay leaves, chicken, lemon zest (NOT the juice), salt and pepper. Lower heat to medium-low and bring to a simmer. Once simmering, or gently bubbling. Cover the pot and allow to simmer for about 15 minutes or until the chicken reaches 175°F-180°F for chicken thighs and 165°F if using breasts.
Once the chicken is cooked, remove it and place on a separate plate to cool and then shred using two forks.
While the chicken is cooling, add the orzo to the simmering pot. Allow it to cook until al dente (it took about 11-12 minutes for mine but this can vary.) When the orzo is done, stir in the parmesan until melted and add the shredded chicken back into the soup. You can add the spinach at this time if using and allow to wilt.
Add more broth if desired if a lot of the broth has cooked off.A few minutes before serving, stir in the lemon juice. Add more lemon zest if desired. Remove from heat and cool for several minutes before serving.