Preheat oven to 375 degrees F. Line a 12-muffin tin with paper liners or spray with flour-based non-stick baking spray.
Combine the oat milk and the apple cider vinegar. Set aside.
In a large mixing bowl, whisk together the vegetable oil and vanilla extract.
In a separate medium mixing bowl, combine the all-purpose flour, granulated sugar, baking powder, salt, and baking soda. Gradually add this sugar/flour mixture to the oil/vanilla mixture. Stir well until combined.
Add the milk and stir just until incorporated. Gently fold in the mashed bananas.
Spoon batter into the prepared muffin tin, filling each cup 3/4 full. Bake in the preheated oven for 25 minutes. Allow the muffins to cool slightly in the tin, for about 5 minutes, then transfer them to a wire rack to cook completely. Serve at room temperature.