Heat oven to the temperature suggested on the cake mix box. Make cake mix according to directions on box by adding in the water, vegetable oil and eggs.
Bake in a 9 x 13 inch pan as directed on cake mix box.
When cake is finished baking and is still warm, poke holes all over cake using a wooden spoon handle or other similar size object (you want those holes fairly big so the pudding has room to get in there and you need to poke straight through to the bottom of the cake).
In a medium bowl, add milk to pudding mixes and continue to whisk until most of the lumps are removed.
Pour pudding on top of warm cake, making sure to pour straight into the holes in the cake.
Take a spoon and spread it evenly across the top of the cake (very gently press down pudding to ensure that pudding goes into the holes and spread it all the way to the sides).
Put cake in fridge and allow to cool completely before adding the frosting (about 2 hours).
Remove the lid and foil covering from the tub of chocolate frosting and microwave for about 10-15 seconds. Stir frosting with a spoon- it should still be thick. Gently spoon or pour chocolate frosting on top of pudding. Spread frosting to evenly cover cake. Start in the middle and gently spread to the sides.
Allow to cool on the counter for a few minutes, then put into the fridge to fully cool and set up.