Preheat oven and prepare cake mix batter according to package directions.

Pour batter into a greased 9×13-inch baking pan.

Bake until a toothpick inserted into the center comes out clean.

Remove cake from oven and allow it to cool completely in pan.

In a mixing bowl, combine sugar-free instant vanilla pudding mix, drained crushed pineapple, and sugar-free Cool Whip.

Stir until the topping is smooth and evenly mixed.

Spread the creamy pineapple mixture evenly over the cooled cake.

Refrigerate the assembled cake for at least one hour to chill and set.

Slice into squares and serve chilled for best texture.