Assault on the Temple of Sha'naar

You receive this quest from the table in the main building of Vol'mar, located just next to Draka.

I'm surprised I don't see more people using this trick.

Deep in the cave is a portal that is being maintained by 4 summoners. Each of the summoners only gives 1% completion to the objective and they drop no loot, so I think that might be a deterrent for some. However, if you kill all four summoners the portal disappears and an elite spawns. The elite gives 6% completion, and when the portal is closed you get a whopping 20% completion to the bonus objective. What's more, the summoners respawn fast enough that you can actually clear them twice before the rest of the trash starts spawning.

Also, if someone else is killing summoners it seems everyone involved gets credit for closing the portal. I had a situation where I only killed one summoner, and someone else got the other 3, but I still got the 20% credit.

So that's 1% x 4 + 20% + 6% = 30% completion remarkably little time. Even with the journey into the cave, this trick makes this Assault quest one of the fastest to complete.

TLDR: Go kill the summoners in the cave. You won't regret it.

If you do not have flying, entrance to the temple is 31,63, by where you are resurrected.