Preheat your oven to 350°F.
In a large mixing bowl, combine the shredded chicken, chopped spinach, cream cheese, sour cream, half of the cheddar cheese, garlic powder, onion powder, salt, and black pepper. Mix until well combined.
Transfer the chicken and spinach mixture into a greased 9x13 inch baking dish.
In a separate bowl, mix the breadcrumbs with olive oil and the remaining cheddar cheese. 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.
Let it cool for 5 minutes before serving.