To create this delicious Chicken and Spinach Casserole, follow these steps:

1. Preheat Oven: Begin by preheating your oven to 350°F (175°C).
2. Prepare Baking Dish: Lightly grease a 9×13 inch baking dish with cooking spray or olive oil.
3. Mix Base Ingredients: In a large mixing bowl, combine the shredded chicken, chopped spinach, softened cream cheese, sour cream, mozzarella cheese, Parmesan cheese, garlic powder, onion powder, salt, and black pepper. Mix well until all ingredients are thoroughly combined.
4. Add Rice or Pasta: If desired, fold in the cooked rice or pasta to the mixture for additional substance.
5. Transfer to Baking Dish: Spoon the mixture into the prepared baking dish, spreading it evenly.
6. Prepare Breadcrumb Topping: In a small bowl, combine the breadcrumbs with olive oil, mixing until they are evenly coated.
7. Top the Casserole: Sprinkle the breadcrumb mixture over the casserole, ensuring an even layer for a crispy top.
8. Bake: Place the baking dish in the preheated oven and bake for 30-35 minutes, or until the casserole is hot and bubbly, and the top is golden.
9. Cool Slightly: Remove the casserole from the oven and allow it to cool for about 5-10 minutes before serving.

This simple yet effective process ensures a wonderfully creamy and flavorful casserole that everyone will love.