Orzo Soak: Preheat oven to 350°F. In a greased 9x13 dish, combine uncooked orzo and warm broth. Let it sit for 30 minutes to soften the grain.
Combine: Stir in the cooked chicken. In a separate bowl, whisk the soup, sour cream, lemon juice/zest, garlic powder, onion powder, pepper, celery salt, parsley, and Parmesan. Pour this over the orzo and stir gently.
First Bake: Sprinkle half of the Swiss cheese on top. Cover tightly with foil and bake for 35 minutes.
Second Bake: Remove foil, give it a gentle stir, and bake uncovered for 25–30 minutes until the orzo is tender.
Crisp & Melt: Increase oven to 375°F. Top with the remaining Swiss cheese and bake for 15–20 minutes until bubbly and golden. (Optional: Broil for 1–2 mins for extra color).
The Wait: Let the dish sit for 15 minutes after removing from the oven. This is crucial—the sauce will look thin at first but will thicken into a perfect consistency as it rests.