How to Make It
In a small saucepan, combine the water with the sugar, the vanilla bean and its seeds and simmer over low heat until the sugar is dissolved. Let cool. Discard the vanilla bean and stir in the lemon juice.
Transfer the mixture to a shallow baking dish and freeze for 2 hours, stirring with a fork every 30 minutes, until the granita is light and snowy. Transfer the granita to a plastic container, cover and freeze.
In a large bowl, combine the orange juice with the sugar, lime juice, ginger, mint and lime zest and stir until the sugar is dissolved. Add the melon balls and let stand at room temperature for 2 hours or refrigerate overnight.
In a small microwavable cup, sprinkle the gelatin over the water and let stand until softened, about 5 minutes. Microwave on high power for 10 seconds, just until the gelatin is dissolved. In a medium bowl, combine the yogurt with the sugar, honey, orange zest and gelatin and stir until smooth. Chill the citrus yogurt just until set, about 30 minutes.
Spoon the yogurt into bowls. Drain the melon balls and mound them on the yogurt. Spoon the granita on top and serve right away.