1. Preheat the oven to 180C/160C Fan/Gas 4 and, using the sunflower oil, lightly grease and line a 900g loaf tin with baking parchment.
2. Put the mashed bananas in you stand mixer and blitz for just a few minutes or until you have a thick liquid consistency and there are still a few bits of banana left. Alternatively you can simply use a fork to mash them up.
3.Add the agave syrup, flour, sultanas, pecan nuts, mixed spice and baking powder.
4. Mix lightly with a wooden spoon until roughly combined, then add the oil and, using a whisk, beat together well for a few minutes.
5. Spoon the cake mixture into the prepared tin and smooth the surface. Add on top two banana halves, and cover the tin with foil, leaving enough room for the cake to rise. Bake for 55–60 minutes, or until a skewer inserted into the centre of the cake comes out a little moist, but clean. As soon as you take it out of the oven, brush the top with a little agave syrup to give it a nice shine.
6. Leave the cake to cool in the tin for 10 minutes, then carefully turn out onto a wire rack and leave to cool for around an hour before serving.