In a medium-sized jar or container, combine rolled oats, chia seeds, unsweetened cocoa powder, and protein powder if desired. Stir these dry ingredients using a spoon or whisk until there are no clumps visible.

Pour in the milk of your choice, Greek yogurt, maple syrup, and vanilla extract into the jar. Blend these wet ingredients into the dry mixture until everything is well incorporated.

Seal the container with a lid or cover it tightly with plastic wrap. Refrigerate for at least 4 hours, preferably overnight.

In the morning, remove your jar from the fridge and give the oats a good stir. If too thick, add a splash of milk and mix until desired creaminess is achieved.

Top with chocolate chips or any other favorite toppings. Enjoy your chocolate overnight oats cold or warmed for a cozy breakfast.