Preheat the oven to 160°C fan/180°C/gas mark 4.
Sieve the flours, baking powder, caster sugar, ground cinnamon and ground ginger in a bowl.
In a separate bowl, mix the oat milk and apple cider vinegar. Set aside for 5 minutes to create a vegan buttermilk.
In another bowl mash the 3 bananas until they form a puree.
Pour the oat milk mixture and banana puree into the flour/spice mix and whisk together until a thick cake batter is formed.
In a saucepan melt together the vegan butter and light brown sugar until a thick sugar paste is formed.
Line a 9 x 13 inch cake tin. Pour the sugar paste into the cake tin. Top with the remaining bananas which are cut in half lengthways.
Spread the cake batter on top of the bananas and place in the oven to bake for 35-40 minutes.
Once baked, flip out onto a plate so the caramel sauce and bananas are on the top.