Preheat the oven to 350°F and prepare a 9x13-inch baking pan with a light coating of cooking spray. Set aside.
In a large bowl, combine cake mix, water, vegetable oil and eggs. Mix until thoroughly combined.
1 (15oz.) box yellow cake mix, 1 cup water, ½ cup vegetable oil, 3 large eggs
Pour batter into the prepared baking pan and bake for 25 minutes or until a toothpick inserted in the center comes out clean.
Allow the cake to cool, then using the handle of a wooden spoon poke holes over each inch of the cake. Set aside.
In a medium bowl, whisk together the pudding mix and milk.
2 (3.4 oz.) boxes instant banana pudding, 2 cups cold whole milk
Spread pudding over cake, pushing over poked holes.
Refrigerate for one hour.
Spread the whipped topping over the pudding layer.
8 ounces whipped topping
Top with crushed vanilla wafer cookies and sliced bananas, if desired.
2 cups crushed vanilla wafer cookies, Sliced bananas