Preheat the oven to 180°C
Sift the flour, baking powder and baking soda, cinnamon and salt into a large bowl.
Mix the butter, sugars, mashed banana, buttermilk, eggs, vanilla extract in another bowl. Add these to the dry ingredients and stir to combine, being careful not to over mix. Fold through the chocolate.
Pour the batter into a non-stick, or lightly greased 19 x 11 cm loaf tin.
Bake for approximately 1 hour or until a skewer comes out clean.
Leave to cool in the tin for a little before turning out onto a wire rack to cool.
To make the cream cheese icing, beat the butter on high speed until creamed. Add the cream cheese and beat on high speed until combined and smooth. Add the icing mixture and salt. Beat on low speed for 30 seconds and then increase the speed a little and beat for a further 1-2 minutes.
Ice the cake and serve in thick slices.