In this case, the chapters in the Cochrane Handbook are each written by a subset of the editorial team for the whole book. I would recommend just citing them as authors (without the editors label for the chapter editors), as they really are functioning as the authors for the specific chapters.

If you want to include the “editors” label for chapter editors, see below:

This is really quite odd to describe the chapter authors as “editors”, rather than “authors” (at least outside of French publishing). Most citation styles won’t be set up to handle this case very easily. The easiest method would be to just enter the chapter editors as Authors and manually add “(editors)” there after you finish writing and unlink the document from Zotero. Another option would be to enter the name of the last chapter editor as “Sterne || JAC (editors)”.

A more involved option would be to enter the chapter authors as “Editors” and then to enter the book editors in Extra like this:
Editorial director: Higgins || JPT

In CSL/Zotero citation styles, “editorial-director” refers to the coordinator of a publication, rather than the textual editor. This is common in French, but rarely in English works, but it can work as a workaround in this case. You would then need to modify whatever citation style file you are using to create the layout for book chapters that have editor and editorial-director variables, but no author variable.

Honestly, that's what they are, and I don't see any reason to cite them as anything else.