In a mason jar or airtight container, combine the rolled oats, unsweetened cocoa powder, chia seeds, and pinch of salt. Stir or shake to mix evenly.

Add the milk, Greek yogurt, maple syrup, and vanilla extract to the jar.

Secure the lid and shake vigorously for about 30 seconds, or stir thoroughly with a spoon until smooth and creamy, resembling brownie batter.

Place the jar in the refrigerator and let it chill for at least 4 hours, preferably overnight, to thicken.

Before serving, stir the oats. If too thick, add a splash more milk to adjust consistency. Top with mini chocolate chips, fresh berries, or nuts as desired.