You need to bring your Wanted level to 5. After one minute the sky will turn red and a dragon will spawn. After the dragon is killed, you get the Achievement.
Tip: Since the enemy is very mobile, it is hard to hit with Iron Man's missiles or Frozone's ice bolts. Attacking with the blasters (first augment of telekinesis) can be very effective.
Tip 2: You can set the difficulty level to "Easy". I don't know if you can get the Achievement on "Immortal" as well.