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.
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)SQL In The Wild
: Discussions on DB performance with occasional diversions into recoverability
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