Cut bread into 1-inch thick slices, without cutting all the way through the loaf. Mix Parmesan cheese, butter, garlic powder, and parsley in a small bowl. Spread mixture between slices of bread and over the top of the loaf. Wrap loaf in aluminum foil, leaving the top partially uncovered.
Bake in preheated oven until butter is melted and bread toasted, 15 to 20 minutes.