Preheat the oven to 180°C and prepare your mould ( mine was 25cm x25cm ).
Mash the bananas, grate the carrots and cut the walnuts.
Mix the flour with baking powder and four spice, and set aside. Mix the eggs with sugar and oil. Mix in the flour.
Add the bananas, carrots, juice, zest and walnuts. Mix well.
The dough is ready for the mould. Bake for 20 mins ( check the middle with a knife, it shouldn't stick ).
You can sprinkle some icing sugar on the top once the cake is baked and rested.