On the Backwater map use your Cloak ability
any enemies while still cloaked. Remember that if you shoot, you will be uncloaked for a short time, stop firing and continue to use melee on any enemies.
To get this quick go into a game of Frontier Defense and choose the map Backwater. Setup a class with Cloak and melee the ground enemies. Using a Ghost burn card will make this very easy.
This is a cumulative achievement and can be done over multiple matches. The achievement will pop after the match.
Any Burn Card that will enhance your cloak and Minion Detector perk are recommended.