Preheat oven to 375°F (190°C).

In a big bowl combine all dry ingredients.

In a medium bowl mash the bananas, leaving some small chunky bits.

Melt you chocolate chips, using a double boiler and set aside.

In a medium bowl, mix oil, yoghurt, and apple cider vinegar - the mix will curdle, which is ok.

Add the wet ingredients to the dry ingredients and combine until just mixed.

Divide the batter into two equal batches. Add the mashed bananas to one halves and the melted chocolate to the other batch.

Using a large spoon, place 3 large spoonfuls of banana mixture into a well greased pan, then 3 spoonfuls of chocolate batter. Repeat with the second layer, alternating the banana and chocolate batter.

Using the handle of a wooden spoon or a knife, swirl the batter to create a marbled effect.

Bake for 45 - 50 minutes.

Let cool in pan on rack for 15 minutes. Turn out onto rack, let cool completely.