Blend one banana, milk, tahini or cashew butter, coffee, dates, cocoa powder, and sea salt together in a blender till smooth. Place the oats and chia seeds in an airtight container. Pour the liquid mixture over the oats and chia seeds, then stir everything well to combine. Cover and refrigerate overnight.
In the morning, stir your oats again and add a small splash of additional non-dairy milk as needed to reach a consistency that you like. Divide the overnight oat base into two serving containers. Slice the remaining banana and add slices to each portion. Enjoy.