Cut the tops off of 12 clementines and reserve the tops. Use a spoon or melon baller to remove the inside of each clementine, adding the insides and all juice to a bowl. Set the empty clementine shells aside. Squeeze the removed insides of the clementines to release as much juice as possible. Discard the pulp and strain the juice. Add juice from more clementines, as necessary, to make up 3 cups.
Peel and puree kiwi fruit to make one cup. Remove any large chunks.
Add 1 cup clementine juice and sugar to a medium saucepan. Bring to a boil over medium heat, stirring frequently to dissolve sugar. Remove from heat and add zest.
Add remaining juice and kiwi puree to the pan and stir to fully combine. Pour the liquid into a baking dish with at least a 2” rim. Freeze for at least 3 hours, scraping the outside edges into the center every 30 minutes with a fork to obtain a flaky consistency.
Fill each of the reserved clementine shells with granita. Add the tops and place on a baking sheet in the freezer until ready to serve. Add mint leaves and tops just before serving.