In a large bowl, combine oats, chia seeds, and cocoa powder. Set aside.
Combine 1 cup unsweetened milk, peanut butter, maple syrup, and vanilla. Whisk to break apart the peanut butter and mix well.
Pour wet ingredients into the bowl of dry ingredients, mix well.
Transfer overnight oats into a glass storage container or jars. Refrigerate overnight.
In the morning - Mix the overnight oats one last time. If the consistency is not as smooth as you’d like, add the additional ¼ cup of unsweetened milk and stir. This will give it a more “oatmeal”-like consistency.
Serve warm or cold with your favorite toppings.