Preheat oven to 165c.
Line a 23cm x 13cm loaf pan with baking paper and set aside
In a large bowl add the bittersweet chocolate and cocoa powder. Pour hot water over both and whisk until smooth and chocolate is melted.
Add sugar, vanilla and melted butter. Whisk to combine.
Add eggs, one at a time, whisking in between each addition until smooth. Add mashed bananas, whisk until smooth and set aside.
Add baking soda and salt and mix well.
Finally add the flour just till it's well incorporated. Do not over-mix.
Transfer batter into loaf pan ¾ of the way full.
Bake the bread for 50-65 minutes or until a skewer comes out clean.
Allow to cool completely and then cut into thick slices.