Gang War

The Protectors of Hyjal is a daily quest obtained at the Sanctuary of Malorne in Hyjal. Just win a duel against someone in Sethria's Roost while on that quest and you've got yourself a shiny new achievement! The person you're dueling can be on the opposing faction and is not required to have the quest in order for you to get credit. While you're there, don't forget to do Have... Have We Met? since both can only be done while on that quest.

These achievements are just two of the many you'll need to get the title: "<Name> the Flamebreaker" from the meta-achievement Veteran of the Molten Front.

Edit: I should add that if you're doing, Have... Have We Met?, you can get credit by waving at NPCs that aren't following you (i.e. NPCs following other people on the quest). So technically, you don't have to be on the quest to get that achievement.

Remember your opponent can just forfeit the duel right after it starts and you'll get the achievement. This way is better than actually dueling to the death with how dangerous the area is (especially on PvP servers).

Just to be clear, only you need to be on the quest. Your duel partner (or should I say victim?) does not need to be on the quest.