Mix the oat flakes and chia seeds in a bowl, pour the milk over them so that the ingredients are just covered, and let soak overnight.
If you like, you can stir in a tablespoon of honey or something similar. The next morning, take the smoothie bowl out of the refrigerator, stir once and serve garnished with the berries.
Tip: It also tastes good with bananas, mangoes and pineapples.