Combine all the ingredients in a mason jar. Mix everything well before you add the water or non-dairy milk. Just add as much liquid to just cover all the ingredients (about 1.5 cup).
Mix again before you refrigerate overnight. Eat it right out of the mason jar the next morning.
You can add some fresh or frozen fruit on top before serving. I personally like blueberries but any fruit will do.
Notes
The banana should add enough sweetness for most people. You could add some maple syrup or vanilla flavor if you desire more sweetness.