Preheat the oven to 375°F (190°C) and grease a 9x13 inch baking dish with non-stick spray or butter.
Place the chopped spinach in a large skillet over medium heat with a tablespoon of water; cook until wilted, then squeeze out all excess moisture thoroughly.
In a large mixing bowl, combine the softened cream cheese, heavy cream, garlic powder, onion powder, salt, and black pepper, whisking until smooth.
Fold the shredded chicken and the drained, wilted spinach into the cream cheese mixture until well incorporated.
Transfer the mixture to the prepared baking dish and spread it into an even layer.
Sprinkle the shredded mozzarella and parmesan cheese evenly over the top of the chicken mixture.
Bake for 25 to 30 minutes, or until the sauce is bubbling and the cheese topping is melted and golden brown.
Remove from the oven and let the casserole rest for 5 minutes before serving to allow the sauce to set.