Grease and line a 2lb loaf tin. Sieve the flour, baking powder and mixed spice into a bowl, then stir in the sugar. Leave on one side.
Place the eggs into the mixer bowl, add the oil and mix with the flexible beater for 2 minutes on speed 4.
Add the dry ingredients, mashed banana and chopped ginger to the eggs and press the fold button 5 or 6 times until the ingredients are well mixed.
Spoon into the prepared tin and bake in the oven for 40-45 minutes until golden brown and well risen (test with a skewer, it should come out clean).
Cool for a few minutes, remove from the tin and remove the paper. Leave to cool completely.
Prepare the topping. Beat the soft cheese, icing sugar and ginger syrup in the mixer bowl with the flexible beater on level 1 for 10 seconds then increase to level 3 for 10 seconds until light and creamy.
Split the cake horizontally into 3 and sandwich together with the filling. Sprinkle with a little icing sugar before serving.