Preheat oven to 375 degrees F (190 degrees C). Prepare a 13x9-inch baking dish with cooking spray.

Mix rhubarb and cherry pie filling together in a bowl; spread into bottom of prepared baking dish.

Stir brown sugar, flour, oats, butter, cinnamon, and nutmeg together in a bowl until crumbly; sprinkle over the rhubarb mixture.

Bake in preheated oven until golden brown on top, about 30 minutes.