Preheat the oven to 350 degrees F (180 degrees C).
Blend the oats, bananas, eggs, cinnamon, maple syrup, and baking powder together until smooth.
Stir in the blackberries until combined.
Pour 1 tablespoon of batter into each cup of a 24-cup silicone mini muffin pan and top with extra chopped blackberries.
Bake the muffins for 15 minutes or until a toothpick inserted comes out clean. If using a normal-sized muffin pan, bake a few minutes longer.
