Sauté the vegetables: Heat 1 tablespoon olive oil in a large pot over medium heat, add 1½ cups carrots, ½ cup celery, ½ cup onion, and 2 cloves minced garlic, cooking for 5-6 minutes until softened.
Add broth and seasonings: Pour in 8 cups chicken broth, then stir in ¾ cup orzo pasta, 1 bay leaf, ½ teaspoon salt, ¼ teaspoon oregano, ¼ teaspoon basil, and ¼ teaspoon thyme.
Simmer until tender: Let your soup bubble gently for 10-12 minutes, stirring once in a while, until the orzo gets tender but still has a little bite.
Optional thickening step: Want it thicker? Whisk together 3 tablespoons melted butter and 3 tablespoons flour, stir into soup, and bubble for 1-2 minutes till it gets creamy.
Add chicken and lemon: Stir in 2-3 cups cooked chicken and ¼-½ cup fresh lemon juice, cook for 2-3 minutes till chicken gets hot and flavors blend together nicely.
Final seasoning and serve: Pull out that bay leaf, taste your soup and add more salt and pepper if needed, then ladle into bowls and top with shredded Parmesan and chopped fresh parsley.