While I wouldn't ever volunteer to adopt a Vegan diet / lifestyle (or even vegetarian, come to that), it is possible to make some pretty good food without using animal products. This unctuous eggless banana cake with a zing of lime is one of those things. Yum!
Preheat your oven to 180°C (356°F).
Make the batter
Mix the flour and sugar together (if you can't get self-raising flour, use plain, all-purpose flour with 1½ teaspoons baking powder). Remove the zest from the lime and squeeze out all the juice.
In a separate bowl, break the bananas into chunks and mash with a fork until you get a fairly smooth paste. Add the oil, lime zest and juice, and stir together. Empty this bowl into the flour and sugar mix and stir well.
Grease a loaf tin with oil and pour in the batter. Bake for 40-50 minutes. Check for doneness by inserting a skewer into the centre of the cake. If it comes out dry, the cake is cooked. Tip out onto a wire rack to cool completely.
Make the buttercream icing
Cream together the sugar and margarine until you have a smooth paste. Stir in the juice and zest of a lime (save 1 slice of lime for decoration if you wish.)
Finish the banana and lime cake
When the cake has cooled, spread a smooth layer of buttercream on the top. You can eat the cake straight away, or leave it in the fridge for half an hour for the buttercream to set.