Break the banana into pieces and place in a bowl. Mash with a fork until the banana has a mushy consistency. Add the oat flakes and pour milk over them. Depending on how liquid or firm the porridge should be, you can vary the amount of milk.
Finally add the blueberries and stir. Place the bowl in the microwave on the highest setting and heat for about 1.5-2 minutes.
If you like, you can stir in a little maple syrup, agave syrup or cane sugar.