Stir together the sugar and water until the sugar dissolves. Put the garlic, ginger, chilli and lime rind into a bowl and pour over the syrup. Put in the refrigerator to cool, then stir through the lime juice and fish sauce.
Meanwhile, cut the squid pouches in half. Score a criss-cross pattern across the inside of the squid with a sharp knife, taking care not to cut all the way through, then cut into bite-sized pieces. Rub the oil over the squid and season well. Cook on a smoking griddle pan for 1–2 minutes until charred and just cooked through.
Put the onion, tomatoes, salad leaves and coriander on a plate. Arrange the squid on top and drizzle over the dressing before serving.