1.Make lemon grass and ginger granita. Place sugar, lemon grass, ginger and the water in a medium saucepan over medium heat, stir until sugar is dissolved. Bring to the boil. Reduce heat, simmer, uncovered, 1 minute. Stand 30 minutes. Strain syrup into a large heatproof jug, stir in juice. Pour syrup into a shallow 1-litre (4-cup) dish. Freeze 1 hour. Use a fork to break up any ice crystals. Freeze a further 4 hours, scraping with a fork every hour, or until frozen.
2.Place fruit and juice in a large bowl, toss gently to combine.
3.Divide fruit salad between serving bowls, top with granita.