Use the tip of a small, sharp knife to score the vanilla pod lengthways through to the centre. Put the sugar and water in a saucepan and heat gently until the sugar dissolves. Halve and deseed the chilli and add it to the saucepan with the vanilla pod. Heat gently for 2 minutes, then remove the pan from the heat and leave the syrup to cool.
Cut away the rind from the clementines and slice the flesh. Remove the stones from the peaches and slice the flesh. Deseed the melon and cut the flesh into small chunks, discarding the skin.
Mix the fruits in a serving dish and pour over the warm syrup, discarding the chilli and vanilla pod. Leave the syrup to cool completely, then cover the fruit salad and chill until you are ready to serve. Decorate with a vanilla pod if liked.