Preheat the oven to 350°F. Line an English cake tin with baking paper.
In a large bowl beat together with a wooden spoon the oil with sugar and agave, add the eggs and vanilla extract and continue to beat until everything is well blended.
Add the flour, baking powder, and salt and mix until you get a smooth batter. Add the mashed bananas – and the optional ingredients – and stir.
Pour the batter into the lined tin, and bake until a toothpick inserted in the center of the cake comes out clean, about 35 -40 minutes. Remove from the oven and let it cool on a wire rack.