Hi there, @gsatutte-bigpond.
I'd be glad to help you get the information of the deleted invoice in QuickBooks Online.
You can use the Audit log to trace the transactions done in QuickBooks. I can show you the steps below:
To know more about the Audit log, you can check out this article: Use the audit log in QuickBooks Online.
I've added a reference which can be handy in the future if you have repetitive transactions such as creating monthly statements to your customers: Create recurring transactions in QuickBooks Online.
You are always welcome to comment below if you have other concerns or questions. It's my pleasure to help. Take care.