Preheat oven to 350°F (175°C). Line a muffin tin with paper liners.
In a large bowl, mix oats, flour, baking powder, baking soda, cinnamon, and salt.
In another bowl, combine mashed bananas, grated apple, honey, milk, oil, egg, and vanilla.
Add wet ingredients to dry ingredients and stir until just combined.
Spoon batter into muffin cups, filling each about ⅔ full.
Bake for 20 minutes or until a toothpick inserted into the center comes out clean.
Let muffins cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.