Peel, pit, and dice the mangos. Blend into a smooth puree in a food processor or blender for at least 1 minute.
Optional: For extra smoothness, strain the mango puree through a fine sieve to remove fibers.
In a large bowl, combine cold water and gelatin. Stir for 30-45 seconds until thickened.
Add sugar, coconut milk, and mango puree to the gelatin mixture. Whisk until smooth.
Transfer to a pot and heat on medium-low until the gelatin dissolves, about 4-5 minutes. Avoid boiling.
Pour the mixture into serving bowls or a silicone mold. Remove air bubbles if necessary.
Chill in the refrigerator for at least 6 hours, or overnight, until set.
Serve chilled with additional evaporated or coconut milk.