Preheat oven to 350°F. Spray a standard 12-cup muffin tin generously with nonstick spray.
In a small bowl, whisk together the oats, baking powder, cinnamon, and salt until well combined.
In a large bowl, whisk together the eggs, milk, mashed banana, and maple syrup until smooth.
Add the melted almond butter to the wet mixture and whisk until no streaks remain. Add vanilla extract and whisk once more.
Pour the dry oat mixture into the wet ingredients. Fold together gently with a rubber spatula until just combined. The batter will look quite wet.
Divide the batter evenly between the 12 muffin cups, filling each about three-quarters full.
Bake for 25 minutes, until the tops are golden and spring back when lightly pressed. A toothpick inserted in the center should come out clean.
Let the cups cool in the pan for 10 minutes. Run a butter knife around each cup's edge and gently lift them out. Transfer to a cooling rack to cool completely.