In a large mixing bowl, combine the cooked rice, chopped spinach, chopped artichoke hearts, shredded mozzarella cheese, grated Parmesan cheese, sour cream, garlic powder, salt, and black pepper. Mix well.
Transfer the mixture to a greased baking dish and spread it out evenly.
Bake in the preheated oven for 25-30 minutes, or until the top is golden and bubbly.
Let it cool for a few minutes before serving. Enjoy!
Notes:
This casserole can be made ahead and refrigerated. Just bake it when you're ready to eat.