View completed tasks by date
 

Is there a way to create a view of completed tasks and the date they were created, across all projects?

You want to show creation date, not completion date? There isn't a way to generate a view in OmniFocus that shows exact creation date for multiple items, because there is no option to show a creation date column. However, you can get an approximate notion of creation date, and use the inspector to look more closely at an individual item.

Go to context mode. Show all contexts. Group by added date. Sort by added date. Show completed actions. Status filter any actions. You'll get a list of all of your completed actions, sorted in reverse chronological order of date they were created, grouped into chunks based on that creation date.

It would be a nice enhancement if OmniFocus allowed one to turn on a column display for any or all of the data it maintains, not just the obvious start, due, completion (especially since it appears that it does not export the other data to a spreadsheet either). Use Help->Send Feedback to make a feature request.