If you're using a cast iron pan make sure to brush with oil in all areas. If you use a baking tin, brush with oil and cover with baking paper. Set aside.
Place the pieces of chocolate, cacao powder and the coconut oil together in a bowl. Melt in a double boiler and leave to cool. Puree the bananas and add to your chocolate mix.
Add banana flour, salt and baking powder in a small bowl and mix through.
Add eggs and vanilla in another bowl and whisk until foamy. First add the flour mixture to your chocolate, then the eggs and mix to a smooth batter.
Place in your pan or baking tin and bake in the oven for about 20-25 minutes or until a wooden skewer comes out clean.