Gather ingredients.

Preheat the oven to 350 degrees F.

Generously grease a 9x13-inch baking pan with cooking spray.

Mix spice cake mix and canned pumpkin together in a large bowl until well combined; spread evenly into the prepared pan.

Bake in the preheated oven until a toothpick inserted in the center comes out clean, about 25 to 30 minutes.

Cool and serve, or store in the refrigerator to serve the next day.