Preheat oven to 180°C.
Line a 7inch dia. baking pan with greased baking paper.
Cut pineapple slices horizontally into 4 slices and place them at the bottom of the baking pan. Place cherries on the pineapples slices.
Mix bake mix, melted butter, milk and water until batter is smooth. Pour batter in the baking pan on top of pineapple slices and walnuts.
Bake for 30 minutes or until a toothpick inserted in the center comes out clean.
Turn the cake upside down while it is still warm. Leave it to cool.