In a bowl or mason jar, combine the oats, cocoa powder, sweetener, vanilla extract, and a pinch of salt.
Pour the milk over the dry ingredients and stir well until everything is fully mixed and the cocoa is dissolved.
Cover the jar or bowl with a lid or plastic wrap.
Place in the refrigerator and let it chill overnight, or at least 6 hours, so the oats absorb the liquid and soften.
In the morning, stir the oats. If the texture is too thick, add a splash of milk to loosen.
Add your favorite toppings such as sliced banana, a dollop of peanut butter, cocoa nibs, or berries.
Serve cold and enjoy!