Preheat oven to 180°C.
Mix bake mix, melted butter, milk, water and sugar until batter is smooth.
Grease and flour a 7inch dia. baking pan.
To make a ring cake grease and flour the outside of a 2inch metal bowl and place it inside the baking pan.
Pour 2/3 of the batter in the outer pan. Add cocoa powder to the remaining batter, mix and put on top of the other batter.
Swirl a fork through the batter for a marble effect and bake for 15 minutes and make a cut around the cake to ensure a crack in the center.
Continue baking for another 15 minutes or until a toothpick inserted in the center comes out clean.