Preheat the oven to 350 degrees F (175 degrees C). Lightly coat the sides of a 9x13-inch baking pan with cooking spray.
Pour cherry filling into the prepared baking pan. Pour water evenly over pie filling. Sprinkle brownie mix evenly in one layer on the top; do not stir it in. Grate frozen butter evenly over the brownie mix.
Bake in the preheated oven until bubbly all over, about 35 minutes. Let stand 10 minutes before serving.