Preheat the oven to 350 degrees F (175 degrees C).
Lightly spray a 9 x 13 inch (23 x 33 cm) cake pan with cooking spray.
Sprinkle the coconut, chocolate chips, and walnuts on the bottom of the pan.
In a medium bowl, mix the cake mix with the oil, eggs, and water until smooth. Pour the cake mix on top of the coconut layer.
Melt the butter and cream cheese in a medium saucepan over medium heat. Add the confectioner's sugar and stir until smooth. Carefully swirl the butter mixture on top of the cake batter.
Bake in the oven until a toothpick inserted into the cake comes out clean, about 35 minutes. Let cool for at least 30 minutes before serving.