This is best done at the start of Chapter 5. From the Medical Tram Station, head over to Imaging Diagnostics. In the back of the room an enemy attached to the wall will continue to spit out pods that will attack with tentacles. Simple let it spit the pods out and stomp (
) on each of them until the achievement unlocks.
The achievement only counts enemies that can be killed in a single stomp. These include the pods shown in the video and the small squid-like enemies with tentacles. The start of Chapter 5 is the first time you encounter this enemy and is the best spot to simply farm the kills for this and all other weapon kills achievements.