In a mixing bowl, combine the chopped spinach, softened cream cheese, shredded mozzarella, shredded cheddar, garlic powder, onion powder, salt, and black pepper. Mix well.
Transfer the mixture to a baking dish and spread it out evenly.
Bake in the preheated oven for 25-30 minutes, or until the top is golden and bubbly.
Remove from the oven and let it cool for a few minutes before serving.
Notes:
This casserole is a great side dish or main course. You can also add cooked chicken or bacon for extra protein.