Preheat the oven to 180°C/Fan 160°C/Gas 4. Rub some oil around the inside of a 500g/1lb loaf tin or insert a baking liner.
Measure the flour and baking powder into a bowl and stir to combine.
Put the brown sugar into a large mixing bowl, add the banana and mash into a paste. Beat in the oil.
Make a tablespoon of fine orange zest strips and set this aside. Finely grate a teaspoon of orange rind and add this to the mixing bowl. Squeeze the orange juice, add it to the bowl and stir to combine.
Sieve the prepared flour blend into the bowl and mix well. Tip the mixture into the prepared tin and smooth the top. Sprinkle the prepared zest strips over the top of the cake.
Bake for 40-45 minutes.