You can get this achievement easily by completing all the contracts at least once on lower difficulties helping you to unlock the fast travel points. Once you completed all the contracts restart the contract from the zone select. You will only need to complete one contract on this difficulty, Antwan Zarza is probably the easiest as you only need to kill 1 enemy at the sniper perch, Antwan Zarza himself, then an easy run back to the exfil point.