Preheat the oven according to the cake mix package directions. Grease a 9 x 13-inch baking pan
Prepare the chocolate cake batter according to the package instructions. Fold in the mashed bananas until evenly distributed
Pour the batter into the prepared pan and bake according to the package directions, checking the center with a toothpick for doneness
Let the cake cool for 10 to 15 minutes
Use the rounded handle of a wooden spoon to poke evenly spaced holes throughout the cake
Whisk the instant banana pudding mix with cold milk until smooth and thickened.
Spoon the pudding over the cake, spreading it evenly and gently working it into the holes.
Cover the cake and refrigerate for at least 2 hours, or until thoroughly chilled
Spread the whipped topping evenly over the chilled cake.
Arrange the sliced bananas over the topping just before serving.
Add chocolate shavings, cookie crumbs, or a light chocolate drizzle if desired.
Slice with a sharp knife and serve chilled.
