Preheat the oven to 375 degrees F (190 degrees C). Spray a 9x13-inch baking dish with olive oil spray.
Pour chicken stock and heavy cream into the prepared baking dish; add orzo, chicken, spinach, tomatoes, 1/2 of the mozzarella, 1/2 of the Parmesan cheese, artichoke hearts, garlic powder, Italian seasoning, salt, pepper, and pepper flakes.
Stir everything together, then smooth the top evenly. Sprinkle casserole with remaining mozzarella and Parmesan cheese.
Bake in the preheated oven, uncovered, until orzo is as tender as you like, 40 to 45 minutes.
Allow casserole to rest for 10 minutes. Stir gently, garnish with fresh parsley, and serve warm.