Preheat the oven to 375°F. Spray a 9x13-inch baking dish with nonstick cooking spray. Set aside.

Place the chicken in a large mixing bowl and season with the black pepper and garlic powder. Add the mayonnaise, Greek yogurt, and Parmesan cheese. Mix with a rubber spatula until thoroughly combined.

Transfer the chicken mixture to the prepared baking dish and smooth it into an even layer. Sprinkle the Parmesan cheese evenly over the top.

Bake the casserole on middle rack of oven until the cheese is lightly browned and the dish bubbles at the edges, 20-25 minutes.

Check to see that casserole is done. Remove from oven or add time as needed.

Allow casserole to rest for 10 minutes before serving. Top with parsley.