Heat the olive oil in a large pot or Dutch oven over medium heat.
Add the chopped onion, carrots, and celery. Cook until the vegetables soften, about 5 to 7 minutes.
Pour in the chicken broth and water. Bring the mixture to a boil.
Stir in the orzo pasta, thyme, and oregano. Reduce the heat to medium-low and simmer until the orzo is nearly tender, about 8 to 10 minutes. Stir occasionally to prevent sticking.
Add the cooked chicken to the pot and heat through for 2 minutes.
Reduce the heat to low. Slowly stir in the heavy cream, lemon juice, and lemon zest. Heat gently for 2 minutes; do not allow the soup to boil after adding the cream.
Season the soup with salt and pepper to your taste.
Ladle the soup into bowls and garnish each serving with fresh chopped parsley.
Notes
For a thicker soup, you can whisk 1 tablespoon of cornstarch with 2 tablespoons of cold water before stirring it into the simmering broth (before adding the cream).
If you prefer a tangier soup, add more lemon juice one teaspoon at a time until you reach your desired flavor.
You can use leftover rotisserie chicken for quick preparation.