Add cherries, water, and coconut sugar to a saucepan and bring to a boil. Reduce to a slow simmer and add cocoa powder. Continue to simmer for 10 minutes, stirring everything together, then remove from heat and allow to cool. Blend until smooth, transfer to a shallow dish, and freeze. Every 30-45 minutes for approximately 3-4 hours, scrape and fluff any frozen bits toward the center of the dish, then return to the freezer. Once ready (there should be no more liquid, only a pile of ice crystals), transfer to a container and seal with a lid (this will keep well for 2-3 weeks).
Optionally, while you wait for the granita to freeze, prepare the whipped cream: Add heavy cream, cream from full fat coconut milk (save the coconut water for another use), and confectioners’ sugar to the bowl of a stand mixer and mix on medium-high until stiff peaks form. Taste and adjust as needed.
When ready to serve, scoop a generous amount of granita into a glass, bowl, or ramekin. If using, garnish with whipped cream, toasted coconut flakes, fresh cherries, and grated dark chocolate.