In a pint size mason jar combine rolled oats, cocoa powder, cinnamon, and chia seeds. Stir in pure vanilla extract, coconut milk, and banana. Put the lid on and place in the refrigerator overnight. In the morning, give the oats a stir. Add in pure maple syrup, if needed, for additional sweetness. Add a little more coconut milk, if needed, to loosen it up and until you get the consistency you want.