Preheat oven to 350 degrees F. Spray a 9x13 pan with nonstick cooking spray.
Add the cake mix to a large mixing bowl and pour in the diet strawberry pop.
Combine by using a handheld mixer at medium speed for two minutes.
Pour the batter into the 9x13 pan. Bake 34-38 minutes or until a toothpick inserted into the center comes out clean. Let the cake cool completely before adding the Cool Whip.
Add the cereal to a zip up bag and use a meat mallet or rolling pin to break down the cereal pieces.
Spread the Cool Whip evenly over the cake. Sprinkle the Fruity Pebbles over the Cool Whip.
If you're not eating the cake right away, wait to add the Fruity Pebbles so they don't become soggy.