There's no easy way (and the link previously given just shows the queries to fetch the missing index information, which is not what was asked)

Grant has, on his blog somewhere, a query to shred the contents of the plan cache (don't do that on prod 🙂 ) to fetch the missing index information and associated queries out of the plans. That, of course, only works if the query is still in cache. If it's not, you're outa luck.