From what I can tell, this cant be done in Practice Mode.
Boot up a match Vs. CPU and set them to Easy. You can choose anyone as an opponent, I personally choose Spinal as he seems to take more damage.
Mira's Health bar will slowly degrade as you damage your opponent and it will have a silver Health Bar underneath it. That's your recoverable damage. If you are attacked by your opponent, you will lose health overall and it will not add to your Recoverable damage, but that shouldn't matter too much.
In order to recover it, you need to use Embrace, which is done by pressing
close to your opponent.
Once you have healed 50%, the achievement will unlock. You won't even need to finish the match.
Enjoy your 10gs
EDIT: As Rat1NaCAG3 has stated, it is possible that you can get this in practice mode.