Preheat oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
In a large bowl, combine sour cream, mayonnaise, garlic powder, onion powder, salt, and pepper.
Stir in the shredded chicken, cooked rice, chopped spinach, mozzarella, and half the Parmesan cheese.
Transfer the mixture to the prepared baking dish and spread evenly.
Sprinkle the remaining Parmesan cheese on top.
Bake uncovered for 25-30 minutes or until the casserole is heated through and the top is golden brown.
Let cool slightly, garnish with fresh parsley if desired, and serve warm.