Make the cake: Preheat oven to 180C (350F). Grease a 8-inch (20cm) round pan and set aside.In a large bowl, place rolled oats, pour in milk and allow to soak for 15 minutes.In a separate bowl, mash bananas, add eggs and whisk until combined. Add cocoa powder, baking powder and mix until combined. At this stage you can add sweetener to make the cake a bit sweeter.Pour soaked oats into the bowl with mashed bananas and mix until combined.Pour the batter to prepared pan and bake for 25-30 minutes or untilAllow to cool for 5 minutes, then release from the pan and allow to cool completely.Make the topping: chop the chocolate and transfer into a heatproof bowl. pour in hot milk, allow to sit for 1-2 minutes and mix until melted and smooth. Drizzle the chocolate over the cake.Chop the nuts and sprinkle over the cake.Serve and enjoy!