Pre-heat the oven to 180°C(fan)/200°C/gas mark 6. Grease a 900g loaf tin and line with baking paper.
First make your flax eggs by mixing 2 tbsp ground flax seeds with 4 tbsp cold water and set aside to thicken. Mash your three ripe bananas in a mixing bowl and set aside.
Whisk together 225g caster sugar and 120ml sunflower oil until smooth. Add 2 flax eggs, 3 mashed bananas, 120ml vegan yoghurt and 1.5 tsp vanilla extract. Beat until well combined.
Use a metal spoon to gently fold in 225g self raising flour, 1.5 tsp bicarbonate of soda and 1.5tsp cinnamon until just mixed.
If using press the two halves of banana into the top of the banana bread before baking.
Pour into the tin and bake for 45-50 minutes. Test with a skewer inserted into the middle - it should come out clean. If the banana bread is getting too brown on top, cover with foil for the last 5-10 minutes of baking.
Leave to rest in the tin for a few minutes and then carefully remove from the tin and leave to cool on a wire rack.