In a sealable glass jar or airtight container, combine the rolled oats, protein powder, chia seeds, and cocoa powder.
Stir the dry ingredients until the protein powder and cocoa are evenly distributed to prevent clumping during hydration.
Incorporate the peanut butter, almond milk, Greek yogurt, and maple syrup into the container.
Stir the mixture vigorously with a spoon or whisk until the peanut butter is fully integrated and no dry pockets remain.
Seal the container with a lid and refrigerate for a minimum of 6 hours or overnight to allow the oats and chia seeds to fully hydrate.
Prior to consumption, stir the mixture once more and adjust the consistency with an additional splash of milk if a thinner texture is preferred.