Select the ebooks in Calibre and drag them to My Library in Zotero. Zotero will fetch their metadata automatically.
(Calibre seems to have a bug that breaks this for certain books with special characters in their titles, so if you're having issues, click the dropdown next to "Save to disk" in Calibre's toolbar, run "Save only EPUB format to disk in a single folder," and then drag the EPUBs from the output folder into Zotero.)
Upgrade Storage
(Calibre seems to have a bug that breaks this for certain books with special characters in their titles, so if you're having issues, click the dropdown next to "Save to disk" in Calibre's toolbar, run "Save only EPUB format to disk in a single folder," and then drag the EPUBs from the output folder into Zotero.)