Preheat the oven to 160°C/325°F/gas 3. You will need a 900g (2lb) silicone loaf pan.
Sift the flours and baking powder into a medium bowl and add 30g of the hazelnuts. Mix the bananas, date syrup, eggs and natural yoghurt in a large bowl until you have a lumpy batter. Add the dry ingredients to the batter and stir until just combined. Pour the batter into the loaf pan. Sprinkle the remaining hazelnuts on top. Bake for 1 hour or until a skewer inserted comes out clean. Set aside to cool for 10 minutes, then remove from the loaf pan and leave to cool on a wire rack.