Line a muffin tin with 8 paper cases. Break 50g of the banana chips into small pieces then mix with the flour, baking powder, lemon zest and muscovado sugar in a large bowl. Whisk the milk, egg and oil together. Mash the bananas with 1 tbsp of lemon juice then fold quickly into the dry ingredients with the egg mixture.
Divide between the cases and bake for 20 minutes at 200C/fan 180C/gas 6 until risen and firm. Cool on a wire rack. Meanwhile mix the icing sugar with 1-2 tsp lemon juice, then dribble over the muffins before topping with remaining banana chips.