Preheat the oven to 375F / 190c.
Prepare the mini muffin pan by greasing with a little oil and sprinkling with flour, knocking off the excess.
Peel and mash the bananas in a large bowl til smooth.
3 overripe bananas
Add the rest of the ingredients to the bowl, except for the blueberries.
1 egg, ¼ cup oil, 1 cup milk, 1 teaspoon vanilla extract, 1 cup all purpose flour, ½ cup rolled oats, 1 teaspoon ground cinnamon, 1 teaspoon baking powder, ½ teaspoon baking soda, ⅛ teaspoon salt
Stir everything together with a spoon until you have a smooth batter.
Add the blueberries to the batter and fold in.
1 cup blueberries
Spoon the batter into the mini muffin cups and place in the preheated oven.
Bake for 14 to 18 minutes until an inserted toothpick comes out clean.
Let cool in the muffin pan for 10 minutes, then run a knife around the edge of each muffin and place on a cooling rack. Once cooled you can store.
Clean the muffin tin, and bake the remaining batter.