Rinse the tapioca pearls under cold water in a fine-mesh strainer until the water runs clear.
In a medium saucepan, combine the coconut milk, sugar, and salt. Heat it over medium heat until warm, but not boiling.
Add the rinsed tapioca pearls to the coconut milk mixture and stir well.
Reduce the heat to low and let it simmer for about 15-20 minutes, stirring occasionally, until the tapioca pearls are translucent and the mixture has thickened.
Once thickened, add the vanilla extract and half of the mango puree (reserve the other half for serving). Stir to combine.
Remove the saucepan from heat and let it cool slightly. Transfer the pudding into serving bowls or cups.
Refrigerate for at least 2 hours to allow the pudding to set completely.
When ready to serve, top each bowl of pudding with the reserved mango puree and diced mango. Garnish with fresh mint leaves.
Notes
Adjust sugar according to the sweetness of the mango puree.