Preheat your oven to 350°F (175°C) and grease a 9x13 inch casserole dish with a little olive oil.
In a large mixing bowl, combine the shredded chicken, chopped spinach, cooked brown rice, cream cheese, sour cream, ½ cup of mozzarella cheese, garlic powder, onion powder, nutmeg, salt, and pepper. Mix well until everything is evenly combined.
Pour the chicken and spinach mixture into the prepared casserole dish, spreading it out evenly.
In a small bowl, mix the breadcrumbs with the remaining ½ cup of mozzarella cheese and olive oil. Sprinkle this mixture evenly over the top of the casserole.
Bake in the preheated oven for 25-30 minutes or until the top is golden brown and the casserole is heated through.
Once done, let it cool for a few minutes before serving.
Notes
Serve hot in the casserole dish garnished with fresh parsley or basil for a pop of color.