Tracer's
Recall ability allows her to go backwards in time to restore her health, ammo & position. In order to unlock this, you will need to recall enough times to gain back 400 health. The recall cooldown is 12 seconds. This is a relatively easy achievement to gain during gameplay by going into battles and immediately recalling as you take damage. The keys here are to play safe in order to stay alive for a long time. Save your blinks to also get out of sticky situations.
An easy way to get is to find an enemy Torbjorn turret or Symmetra Sentries. This will automatically shoot at you and deal damage. All you want to do is poke out in front of them, take damage and recall. Rinse and repeat until it unlocks.
If you'd like to learn more about tracer and this achievement, you can view this video: