Take the mango chunks and freeze the fruit for about four hours, until slightly hardened.
Put the frozen mango, simple syrup (if using) coconut milk, and ice in your blender. Blend until smooth! Serve immediately.
Note: You can buy simple syrup pre-made, but if you'd like to make it yourself, simply mix together equal parts water and sugar (however much you'd like), and dissolve in a saucepan over medium heat. Cool completely.