Preheat the oven to 180 celsius (350 fahrenheit) and grease 1 large loaf tin.
In a large bowl of an electric mixer fitted with a paddle attachment cream the butter and caster sugar until pale. Add the eggs one at a time and mix well before adding the banana and vanilla.
Switch off the mixer and sift in the flour and baking powder and fold through using a wooden spoon or spatula. Add the banana slices, chocolate, hazelnuts and yoghurt and fold through until just combined.
Pour the mixture into the prepared loaf tin and then trim a piece of baking paper to size and place of the top of the loaf. Bake for 30 minutes before reducing the temperature to 160 celsius (320 fahrenheit) and baking for a further 30 to 40 minutes, or until a cake tester comes out cleanly.
Remove from the tin and place on a wire rack to cool.