Preheat the oven to 350F and grease an 8×4 loaf pan and set aside.
In a large mixing bowl, mash the bananas until no large chunks remain and add in the melted butter, brown sugar, and vanilla. Stir to combine. Add in the flour, oats, baking powder, baking soda, salt, and dash of all spice. Mix together. Fold in the blueberries.
Pour the batter into the prepared loaf pan and bake for 50-60 minutes until the top is golden brown and an inserted toothpick comes out clean.