Begin by preheating your oven to 350 degrees F. Line muffin pans with baking cups and set aside.
In a large bowl, mash the bananas with a fork or electric mixer. Add the honey, butter, flaxseed, eggs, and vanilla. Mix until thoroughly combined.
In a separate mixing bowl, whisk together the flour, sugar, oats, baking powder, baking soda, and salt. Add this mixture of dry ingredients to the wet ones and mix until almost incorporated. Then fold in the blackberries.
Divide the batter among the prepared muffin cups. Sprinkle each with additional oats.
Bake for about 30 minutes or until the tops start to brown and a toothpick inserted near the center comes outs clean. When perfectly done, remove the muffins from the oven. Allow the muffins to rest in the pans for 5-8 minutes before transferring to a wire rack to cool completely.