Ok, if you are not a PvPer then this can be difficult to get against another player. Most who play the PvP element of this game have been doing so for a long time and will likely have better skills/gear/rotation.
Which is why we aren’t going to go anywhere near another player. Well, aside from those on your team.
Get yourself in a guild, head to the Imperial City with a group of 3 or 4 of you and find one of the patrolling horrors. When they die they drop a significant amount of Tel Var. The key here is to kill 3 or 4 of the horrors without dying. The more Tel Var you have on your character, the larger a multiplier you will have, so each subsequent horror will drop more Tel Var. Just keep killing them until you get your achievement.