Pre-heat the oven to 180ºC.
Grease and line a 20cm baking tin.
Remove the pit from the dates and soak the dates in boiling water for 5 minutes.
Add the vinegar to the soy milk and leave it to rest.
In a food processor, add the banana and process until it breaks down.
Drain the dates and add to the banana. Process until there aren't any big chunks.
Add the eggs, coconut oil, vanilla extract and curdled soy milk and mix.
Add the dry ingredients, except the cocoa powder, in a bowl and mix it together.
Pour the banana mixture in the dry ingredients until fold them until they are incorporated.
With a spoon, add half the mixture in splodges on the baking pan.
Mix the cocoa and do the same with the remaning mixture.
Marble it with a toothpick or a knife.
Bake it for 40 minutes and leave it to cool down.