Not very easily. Note, first, that you most likely only deleted the collection, no the items _in_ the collection. The items are still under "My Library".
You can try this if you really need the collection back:
https://www.zotero.org/support/zotero_data#restoring_from_the_last_automatic_backup
Are there any plans to add the option to undo deleting collections?
This seems to be a problem that occurs very often and can create quite a bit of havoc, especially when you use collections to organize large amounts of information. (I'm speaking from experience.)
I honestly do not understanding why this feature is still not there in Zotero, given that the disastrous consequence that an accidental deletion might have on large collections.
Upgrade Storage
You can try this if you really need the collection back:
https://www.zotero.org/support/zotero_data#restoring_from_the_last_automatic_backup
This seems to be a problem that occurs very often and can create quite a bit of havoc, especially when you use collections to organize large amounts of information. (I'm speaking from experience.)
PLEASE IMPLEMENT THIS FEATURE ASAP!