This achievement is relatively easy.
The second Decepticon mission has plenty of Cloakers in it. Play as Starscream since he has a sniper-type weapon, Null Ray I believe it is called. After you finish the section with the Autobot floating platform that is projecting a shield over a doorway, you'll come across your first Cloaker. Follow him into a room that will have several in it. You'll be able to tell where a Cloaker is by his charging Plasma Cannon. Hold the Left Trigger button to go into sniping mode. Find one that is charging his Plasma and aim just a little bit higher and to the right of it (if you are head-to-head) and pop a shot off.
I was able to do this on Hard and it basically one-shotted the Cloaker.