Pre-heat the oven to 175 degrees Celsius. Grease a 9x5-inch loaf tin and line the bottom with a greaseproof paper.
Whisk the flour, baking powder, baking soda, salt, cinnamon together in a small bowl. Set aside.
Combine the Nutella and honey in a medium bowl. Microwave for 30 seconds on high till the mixture has melted and is smooth. Alternatively, place the bowl over a pot of simmering water and stir until the mixture has melted and is smooth. Let the mixture cool slightly.
Combine the mashed bananas, yogurt, egg and vanilla in a large bowl with a wooden spoon then stir in the cooled Nutella-honey mixture. Sift in the flour mixture and stir it in gently. Transfer the batter into the greased tin and sprinkle the almond flakes and sugar evenly over the top of the batter.
Bake the loaf for 50 to 60 minutes, until a skewer inserted into the centre of the loaf comes out clean. Tent the tin with aluminium foil if the top is getting too browned. (I tented mine after 40 minutes of baking, and continue baking the loaf for 20 more minutes.)
Cool the loaf in the tin on a wire rack for 10 minutes, then turn it out and let the loaf cool completely on the wire rack before serving.