Place the lime juice, passion fruit juice and seeds, and ginger cordial in a small saucepan.
Place the lemon grass in a small food processor and blitz until finely chopped, then add to the pan and heat for 2-3 minutes. Leave the syrup to cool slightly.
Meanwhile, mix the fruits together in a bowl and pour over the syrup. Allow to marinate for about 1 hour. Serve with a scoop of coconut and lime ice cream.