This can be done fairly early on and pretty much in the same area as the 'Blast Radius' achievement. Once you've thrown the grenade, walk around the corner and you'll see more Swarm CELL and there should be more than enough of them to kill.
To slide you need to first sprint by pressing and holding in then while sprinting hold down to slide for a period of time. What gun you use doesn't matter, though some on certain targets are better, like the shotgun. I simply just kept sliding in this corridor with my assault rifle and killed all the Swarm CELL and the achievement unlocked!