Preheat your oven to 350°F (175°C) and spray a 9×13-inch baking pan with cooking spray.
In a large bowl, combine the canned pumpkin and spice cake mix. Stir until the batter is smooth and well incorporated.
Spread the batter evenly into the prepared pan, smoothing the top with a spatula.
Bake for 25–30 minutes, or until a toothpick inserted in the center comes out clean.
Allow the cake to cool completely before slicing.
Top with your favorite cream cheese frosting or a dusting of powdered sugar before serving.