This achievement should easily be done in less than 10 minutes. Simply play some campaign missions, or play PvP battles. In one battle/missions, the enemy has between 1-5 units. This achievement will take around 5-10 battles to get. The first couple of campaign missions are very easy to do. Simply select auto-deploy, and win the battle. Should be no big deal to get this one.
You can see your progress if you press Tools-> Achievements.