In a mixing bowl, combine the rolled oats, coconut milk, chia seeds, honey (or maple syrup), vanilla extract, and a pinch of salt. Stir well until everything is evenly mixed.
Fold in half of the diced mango into the oat mixture, reserving the other half for topping later.
Divide the mixture evenly into two jars or containers with lids. Seal them and place in the refrigerator overnight (or for at least 4 hours) to allow the oats to soak up the liquid and thicken.
In the morning or when ready to serve, remove the jars from the fridge and give the oats a good stir. If the mixture is too thick, add a splash of coconut milk to achieve your desired consistency.
Top each serving with the remaining diced mango, a sprinkle of toasted coconut flakes, and a few fresh mint leaves for a pop of color and freshness.