To get this simply make sure to equip the Support Class such as Díaz.
Next swap the frag nades for the Sim nades.
Find a 1 or more locusts. Switch to the snub or simply shoot to NOT kill.
Lastly with the medic class throw the healing nade at the locusts.
(You can try to simply throw it a pair of locust. On my game the achievement popped simply because I threw the nade at full hp locust. If this doesn't work Simply do some chip damage and try again.. Apologies some of the achievements. Can pop late)