Prepare Ingredients
Preheat oven to 375°F.
If using rotisserie chicken, shred or dice it into bite-sized pieces. If using fresh spinach, give it a rough chop. For frozen spinach, ensure it's completely thawed and well-drained.
Mince garlic cloves finely. Halve cherry tomatoes if desired. Grate parmesan and shred mozzarella if not already prepared.
Combine Base Ingredients
In a large 9x13-inch baking dish, add dry orzo pasta and spread evenly.
Add cooked chicken pieces, distributing them throughout the orzo.
Scatter chopped spinach over the orzo and chicken.
Add cherry tomatoes (whole or halved) and sprinkle minced garlic evenly over everything.
Create Creamy Sauce
In a large mixing bowl or measuring cup, combine chicken stock and heavy cream. Whisk until fully blended.
Add Italian seasoning, salt, and freshly cracked pepper to the liquid mixture.
Squeeze juice from half a lemon into the liquid and stir until seasonings are evenly distributed.
Add Liquid and First Cheese Layer
Pour liquid mixture evenly over the orzo, chicken, and vegetables in baking dish. Ensure liquid covers the orzo completely. Gently press down ingredients if needed so they're submerged.
Sprinkle grated parmesan cheese evenly over the top. Reserve mozzarella for later.
Bake Covered
Cover baking dish tightly with aluminum foil.
Place in preheated oven and bake for 30 minutes.
Add Mozzarella and Finish Baking
After 30 minutes, carefully remove dish from oven and remove foil (watch for hot steam). Orzo should be tender and most liquid absorbed.
Sprinkle shredded mozzarella cheese evenly over the top.
Return dish to oven, uncovered, and bake for an additional 10 minutes, or until cheese is melted, bubbly, and lightly golden.
Rest and Serve
Remove from oven and let rest for 5 minutes before serving.
Garnish with fresh basil or parsley if desired. Serve hot.