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How to make turkey burgers
Grate the onion.
Take half a medium onion, and use the fine side of a grater to grate the onion. You should wind up with approximately 2 tablespoons (30 g) of grated onion, as well as some juice, which you can discard.
If you don't have a grater, you can finely dice the onion with a knife. Keep in mind that the onions will be more noticeable in the finished burgers if you dice instead of grating, though.