Preheat the oven to 375 degrees and lightly grease a 9 by 13 inch baking dish.
In a large mixing bowl, combine the shredded chicken, cooked rice, chopped artichoke hearts, and chopped spinach.
Add the softened cream cheese, sour cream, garlic powder, salt, and black pepper to the bowl. Stir until the mixture is evenly coated.
Fold in half of the mozzarella cheese and all of the Parmesan cheese.
Spread the mixture into the prepared baking dish and smooth the top.
Sprinkle the remaining mozzarella cheese evenly over the surface.
Bake for 25 to 30 minutes until the cheese is melted and the edges start to bubble.