Prepare crumb topping by combining all the ingredients together cutting them together with a fork or pastry cutter until a coarse crumb forms. Set aside.
Preheat oven to 180 celsius. Prepare an 8x8 baking pan by lining it with a sheet of parchment paper, leaving a few inches of overhang on the sides to allow for easy removal. Set aside.
In a large bowl mash bananas. Whisk in all ingredients util well combined.
Pour the batter into your prepared baking pan, using a spatula to distribute it evenly. Top with the crumb topping and bake for 50 minutes until the center is set and a toothpick comes out clean. Cool for 10 minutes. Dust with some cinnamon and sliced banana.