If the mango chunks are in large pieces, chop them into smaller, 1/4-inch pieces. Place half of the mango chunks , the coconut milk, and sugar in a blender and process until smooth.
Divide the remaining mango chunks between 4 small containers (10-12oz. containers). Add 1.5 Tbsp of chia seeds to each container. Finally, pour the mango coconut milk mixture into the containers, dividing it evenly between all four.
Stir the contents of each container to make sure all the chia seeds have adequate exposure to the liquid. Place lids on the containers and refrigerate over night, or up to 4-5 days.
*Fresh mango can be used in place of frozen. You'll need about 2 cups of mango chunks. **Do not use full-fat canned coconut milk as it has a lower moisture content and may not fully hydrate the chia seeds.