Pre-heat the oven to 190C/375F. Line a 12-cup muffin tin with muffin liners or coat well with cooking spray. Set aside.
In a large bowl, mix together the dry ingredients - all-purpose flour, oat flour, whole oats, baking powder, baking soda, salt, cinnamon.
In a medium bowl, mash the bananas with a fork or potato masher until it forms a uniform consistency.
Add in the rest of the wet ingredients - egg, honey, vanilla extract, oil and greek yogurt. Whisk until well combined.
Add in about half of the dry ingredients into the wet mixture and stir until all well combined. Repeat with the rest of the dry ingredients. Don’t overmix, as it can affect the baking process.
Once all the dry ingredients have been combined, gently fold in the blackberries with a spatula.
Spoon the muffin batter evenly into the muffin cups, filling them up to around ¾ of the way. Top them with some additional rolled oats.
Bake for 20-25 minutes or until the top is golden brown and a toothpick poked into the center comes out clean. Set aside to cool on a wire rack for at least an hour before eating.