Pour coconut milk into a medium-sized bowl. Whisk together with a fork until the consistency is uniform (it will initially be part solid, part liquid). If using sweetener, add it now and mix until fully combined.
Add chia seeds and continue to whisk for a good 2 minutes, until chia is fully immersed and spreads out in the liquid. Cover and refrigerate for at least 4 hours to thicken. It will become like tapioca pudding.