Prepare cake in a 9x13 pan according to directions on the box.
Once baked, allow to cool for about 5-10 minutes.
Using the back of a spoon, poke several holes into the top of the cake.
Prepare pudding by combining the pudding mix and milk together in a bowl with a whisk until no lumps are present.
Evenly pour pudding mixture on top of cake filling each of the holes.
Place pan into refrigerator for at least 2 hours, or until set.
Spread whipped topping evenly on top, followed by the crush wafers.
Finish the cake by placing the banana slices on top as desired.
Serve and enjoy! Be sure to refrigerate any leftovers!