First, wash and dry your chicken. Cut into 1-inch chunks, and season with salt and pepper.
In a medium-large frying pan, heat 1 tablespoon of olive oil. Add your chicken chunks, and cook until lightly browned. Transfer to a bowl and set aside.
Add the remaining 1 tablespoon of olive oil to a large pot, and add the onion, garlic, celery and carrots. Stir and cook over medium heat for 3-4 minutes, until tender. Add the dried thyme and lemon zest, and cook for 1 more minute.
Add the broth, bay leaf, and 1 cup water to the pot, and bring to a boil. Once boiling, add the orzo, cooked chicken and rosemary sprig.
Reduce heat and simmer for 10 minutes, or until the orzo is cooked through.
Remove from heat and stir in the lemon juice, and salt and pepper to taste.
Serve immediately and enjoy.