Pre-heat oven to 180°C /350°F (convetional) or 160°C / 320°F (fan) and line a 6-cup bread tin with baking paper.
In a large bowl, mash the bananas well. Whisk in the milk, sunflower oil, vanilla, yoghurt, and sugar. Stir in the baking soda.
In a separate bowl combine the flour, cinnamon, baking powder and salt.
Add the wet ingredients to the dry and stir until just combined - don't overmix. Fold in the chocolate chips.
Spoon the banana bread batter in to the lined bread tin.
If adding the oatmeal crumble, combine the topping ingredients in a small bowl and using your fingers massage the mixture until the butter binds the mixture in to a crumble texture. Sprinkle the topping over the top of the vegan banana bread batter.
Pop the bread tin in the oven and bake for 50 - 60 minutes or until a skewer comes out of the centre of the loaf clean.
Remove the bread from the oven and allow it to sit for 15 minutes before turning out.
Serve warm or cold.