Peel and cut the flesh away from the mangos. Dice one of the mangos and set it aside. In a blender or food processor, blend the other mango. The mango puree should be ~1 cup, and together, the mango puree and coconut milk should make 1.5 cups. If less, add more coconut milk to make at least 1.5 cups total.
Transfer the mango puree and coconut milk to a small bowl. Stir in the chia seeds until well combined.
Stir the diced mango in now, or set it aside until you're ready to serve, if you want to top the chia pudding with it. Cover and set in the refrigerator overnight, or for at least 2 hours. Once it's ready, stir the chia pudding and divide between four glasses.