[header] How to make turkey burgers [title] Grate the onion. [step] 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. 
[substeps] 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.