Oysters with Green Apple and Wasabi Granita

In a blender, combine the apple juice, sugar and wasabi and puree until smooth. Strain through a fine sieve into a 2-cup baking dish; discard the solids. Stir in the food coloring, then freeze for 30 minutes. Using a fork, stir the granita; continue freezing and stirring every 30 minutes, until frozen and fluffy, about 3 hours. To serve, spoon 1 teaspoon of the granita onto a shucked oyster and garnish with micro nasturtium leaves.