Add the rolled oats, the coconut milk, the chia seeds, and the cinnamon to the bowl and stir until all the ingredients are combined.
Peel and cut one of the mangoes into chunks and add the mango pieces to the oatmeal mixture. Fold the mango chunks into the oatmeal mixture.
Cover the bowl with a lid or some plastic wrap and place the bowl in the fridge overnight.
In the morning, add another 1/4 - 1/2 cup coconut milk to the mixture, just to loosen it up a little bit. Divide it between 2 mason jars.
Peel and cut the other mango into chunks and top the oatmeal mixture in both jars with the fruit. Add some toasted unsweetened coconut to the top and enjoy immediately, or place the lids on the jars for a delicious and healthy breakfast that's perfectly portable!