Preheat your oven to 375°F (190°C) to ensure it's hot and ready for baking.
In a large skillet, heat the olive oil over medium heat. Add the chopped spinach and sauté for approximately 3 minutes, or until the spinach has wilted and reduced in volume. Once done, remove the skillet from heat and set the wilted spinach aside.
In a spacious mixing bowl, combine the shredded chicken, the sautéed spinach, softened cream cheese, shredded mozzarella, sour cream, garlic powder, onion powder, and season with salt and pepper to taste. Using a spatula or wooden spoon, mix everything together until the mixture is smooth and well-combined.
Grease a 9x13 inch baking dish with a little olive oil or cooking spray to prevent sticking. Pour the chicken and spinach mixture into the dish, spreading it evenly to cover the bottom.
If you desire an added crunch, sprinkle breadcrumbs evenly over the top of the mixture. This step is optional but highly recommended for texture!
Sprinkle the grated Parmesan cheese generously over the breadcrumbs or directly on the mixture if omitting them.
Place the assembled casserole in the preheated oven and bake for 25-30 minutes. Keep an eye out for the cheese to become bubbly and golden brown, indicating that the dish is ready.
Once out of the oven, allow the casserole to rest for about 5 minutes before serving. This will help it set up a bit and make it easier to scoop out portions.
Notes
Serve hot, garnished with freshly chopped parsley or basil.