Simply load up the "Tatooine" level and after defeating the hacked Purge Troopers you will make your way to the Garbage Processing Room. You will find an unlimited spawn of Jawa's and must use the Force to crush them in the grinder.
It can be a bit tedious as sometimes your throw kills them or it will die from the force and not the grinder but as it is an unlimited spawn you will get it down.
I created this video to help:
Hope this helps.