Put the oat flakes with the milk in a bowl and sprinkle the blueberries on top. Let stand for 12 hours, i.e. overnight.
The next day, if necessary, sweeten with a little honey and enjoy as a quick, filling breakfast.
Variants: Since I like cinnamon, it was added on top. You can just as easily change the recipe as you like, e.g. with different milk, other berries, nuts instead of berries or the like.