Preheat oven to 180°C. Line ten 250ml (1-cup) capacity muffin pans with paper cases. Sift the flour and baking powder into a large bowl. Stir in the sugar. Make a well in the centre. Add the egg, banana, lemon rind, lemon juice, oil and milk. Stir until just combined.
Divide the mixture among the prepared pans. Bake for 20 minutes or until golden. Set aside in the pans for 10 minutes to cool slightly before transferring to a wire rack to cool completely.
Use an electric beater to beat the cream cheese, peanut butter and icing sugar in a bowl for 4 minutes or until pale and creamy.
Spread icing over muffins and top with banana chips.