Disintegration

As soon as you get a mission with Doyle (chunky boy Robot) in your Squad (First one is Mission 2 I believe). Just find a group of clustered enemies and use his ability on them. Reload the checkpoint if you want to knock it out real quick and hope the autosave (they show up as a message on the HUD) was close enough to the group you just encountered OR just keep using the ability normally throughout the campaign and its pretty much an unmissable achievement. Make sure you use the targeting method where you activate the ability with one button and then confirm it with another as that one will put the game on ultra bullet time so you can perfectly line up the shot and get the most out of it.