Preheat oven to 350°F. Coat a 12-cup muffin tray with cooking spray.
Combine 1 ¼ cups oats, whole-wheat flour, all-purpose flour, cinnamon, baking soda, baking powder and salt in a medium bowl; whisk until well mixed.
Combine bananas, milk, oil, honey, eggs and vanilla in a large bowl; beat with an electric mixer on medium speed until well combined, about 1 minute.
Add the flour mixture to the banana mixture; beat on low speed until just combined and a thick batter forms, about 45 seconds, stopping to scrape down the sides as needed.
Spoon the batter into the prepared muffin cups (a scant ⅓ cup each). Sprinkle the tops with the remaining ¼ cup oats. Bake until golden and a wooden pick inserted in the center comes out clean, about 18 minutes. Let cool in the pan for 10 minutes; serve warm.
