Preheat oven to 350˚F. Butter a loaf pan. (Optional: prepare streusel.)
In a mixing bowl (or processor), mash sugar, oil, egg, and browned bananas.
Add vanilla and milk and mix to combine.
In a measuring cup, stir together oat/almond flour, all purpose flour, baking soda, baking powder, and cinnamon.
Add the flour mixture to the banana mixture with some crushed nuts or chocolate chips, and stir until just combined.
Pour into buttered loaf pan, top with streusel, and bake at 350˚F until brown on top and cooked through, about 55 minutes.