Step 1

Preheat the oven to 350 degrees F (175 degrees C). Spray a 9x13-inch baking pan with cooking spray.

Step 2

Blend cake mix, water, egg whites, and oil in a bowl using an electric mixer until moistened. Pour batter into the prepared pan.

Step 3

Bake in the preheated oven until a toothpick inserted into the center of the cake comes out clean, 23 to 28 minutes.

Step 4

Poke holes into the hot cake. Pour in pina colada mix and sweetened condensed milk. Let cool completely, at least 2 hours.

Step 5

Spread whipped topping over cake. Sprinkle coconut on top. Refrigerate until ready to serve.