Miasma Chronicles

A great early game place to unlock this achievement and many others is during the side quest "the ritual of wood" which sees you fight in a small space against the Whisperer enemies

The whisperers spawn in 6 spawnlings right at the start of the fight simply bunch them up and you can unlock this achievement with a well placed grenade

here's a visual reference

https://youtube.com/shorts/ukMMvpX4orc