Butter a 9x5 loaf pan. You could also line with parchment paper and spray with baking spray. Preheat the oven to 350 degrees.
In a large bowl, mash the bananas. Add in the oil, sugar, eggs, vanilla and stir together until combined. Fold in unfed sourdough starter (you are using the discard, the starter is not fed) and coconut milk yogurt (if you’re using).
In a separate bowl, whisk together the flour, sea salt, baking soda and baking powder.
Add dry ingredients to wet and stir until combined.
Transfer batter into the loaf pan and sprinkle cinnamon sugar on top. Bake for 55-60 minutes, or until a tester inserted in middle comes out clean. Let cool in pan for 10 minutes and then gently remove onto a wire rack to thoroughly cool.