In a small bowl, whisk together the oat flour, maca, baking powder, and ¼ teaspoon salt to combine.
In a medium bowl, whisk together the milk, melted butter, egg yolks, maple syrup, and vanilla extract. Stir the dry ingredients into the wet ingredients until just combined.
Preheat waffle iron to high. In a separate medium bowl, using a hand mixer, beat egg whites to stiff peaks. Fold whites into batter until just combined.
When the iron is hot, brush it with melted butter. Then, pour half the batter into the waffle iron and cook until lightly golden, about 4 minutes. Transfer to a plate and repeat with remaining batter.
Top each waffle with half the banana slices, cacao nibs, and a drizzle of melted chocolate. Serve with additional maple syrup, if desired.