As pointed out in your link, true capers are the flower buds of the caper plant. But a friend of mine, or maybe my mom, years ago tried Nasturtium seeds and they were not bad. I have a lot of nasturtiums in the garden and the frosts are beginning here so when I pull them out I might try that. You can also use nasturtium leaves and flowers in salads - crisp peppery taste.
Any pointers to good Bagels in Sydney will be gratefully received!