Preheat the oven to 375°F. Grease a standard muffin tin, or line with papers and grease the papers., Combine the yogurt, egg, oil, mashed banana, sugar, and oat bran in a bowl. Whisk together and set aside for 10 minutes., Whisk together the flour, baking powder, salt, baking soda, and nutmeg., Work the topping ingredients together until the mixture is crumbly., Whisk the banana mixture into the flour mixture. Scoop into the prepared muffin cups, filling them almost full; the muffins won't rise much., Sprinkle muffins with the topping., Bake the muffins for 20 to 24 minutes, until the muffins are set and browned. Remove from the oven and let rest in the pan for 5 minutes. Remove from the pan and enjoy warm.