They're so tied to the south that they're jokingly called 'Southland sushi', and cafés elsewhere in New Zealand often don't sell them at all.
White bread is spread with a savoury cheese-and-onion-soup filling, rolled up, buttered and toasted until the outside turns crisp and golden and the inside goes molten. They're sold by the dozen at Southland and Otago bakeries, dairies and school fundraisers, cheap enough to buy by the bagful.