Combine the oats, brown sugar, cinnamon, and salt in a small bowl. Give the ingredients a quick stir to mix everything together.

Pour the melted butter over the dry ingredients and toss until all the ingredients are well coated and moistened. Set the topping aside and make the muffin batter.

Preheat the oven to 400° and line a muffin pan with paper liners. Give the top of the muffin tin a spritz of cooking spray, so that the muffin tops don't stick, this is optional, but helpful later.

In a medium sized bowl, add the oats,  all purpose flour, baking powder, baking soda, salt, and cinnamon. Whisk to get all the dry ingredients combined. Set aside.

In a large bowl, add your mashed bananas and sugar and whisk them together.

Add in the egg and the vanilla and whisk until well incorporated.

Next, grab the melted butter and drizzle it into the banana and egg mixture. Whisk while you drizzle to evenly distribute the butter into the wet ingredients.

Pour the dry ingredients into the wet ingredients. Using a rubber spatula or a spoon, stir the batter until almost fully mixed. but stop when the batter looks lumpy with some flour streaks still remaining.

Add the blueberries to the lumpy batter. Quickly and gently, fold the berries into the batter until the berries are evenly distributed and no flour streaks remain. Do not overmix.

Divide the batter between the 12 muffin cups.

Grab your oat muffin topping and generously distribute it over the muffin batter.

Bake at 400° for 20-25 minutes*. The muffins are done when a toothpick inserted comes out clean.

Remove the muffins from the oven and allow them to cool down enough to be handled, but still very warm. Carefully take the muffins out of the pan and set them on a cooling rack to finish cooling. Taking the muffins out of the pan while warm will help keep the tops from sticking to the pan. Serve and enjoy!