This achievement could be easily marked as story related since you come across it during the temple district main story progression.
Without giving away much spoilers, the second main quest will lead you to the temple district where you have to rescue 4 priests. The 4th one is being interrogated in the middle of the district, you just have to follow the quest to get there.
After you fight with the interrogator and adds the boss, Uzuruz will take the stage. Unfortunately I don't have a full strategy to him as a random person helped me out on this one, but he has a large AoE attack that can one shot a lowly DPS like me. Otherwise he doesn't seem to have a particularly large health pool.