Heat 1 tablespoon of oil in a large, heavy-bottom stock pan over medium heat. While the oil is heating, season the cubed chicken with kosher salt and pepper, then add it to the pan. Cook the chicken until golden on each side. Once seared, remove the chicken from the pan, place it on a plate, and set aside.
If the pan is dry, add the remaining 1 tablespoon of olive oil. Add the diced onions, carrots, and celery, and sauté until the onions are translucent and softened, about 3-5 minutes. Stir in the garlic and thyme and cook for 30-60 seconds, until lightly toasted.
Add the dry white wine (or additional stock) and scrape up any browned bits off the bottom of the pot. Let it simmer for 1-2 minutes to reduce by half.
Add the chicken stock, bay leaves, and crushed red pepper flakes to the pan, stir, and bring the mixture to a boil.
Once boiling, return the chicken and any accumulated juices to the pot, along with the uncooked orzo. Reduce the heat to medium and simmer, stirring every minute or so, until the orzo is tender, about 9-10 minutes.
Turn off the heat and stir in the lemon zest and lemon juice. Taste to adjust seasonings.
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Notes
Wine: Use a dry white wine suitable for drinking, such as a Pinot Grigio or Riesling. Otherwise, use additional stock. Thyme: If you don’t have fresh thyme, use ½ teaspoon dried thyme leaves. Do not use ground thyme.Crushed Red Pepper Flakes: Omit, or reduce, the red pepper flakes if you are sensitive to heat.Using Leftover Cooked Chicken: Reduce the olive oil to 1 tablespoon, skip searing the chicken, and add 3-4 cups of shredded or diced cooked chicken to the soup for the last 5 minutes of simmering, just to warm it through.Storage: Store the leftover soup in an airtight container in the refrigerator for 3-4 days. Alternatively, store the leftover soup in a freezer-safe container, leaving a 1-inch space for expansion, for up to 3 months. When reheating, thin out with broth or water as needed, adding a pinch of salt to help season.