Disintegration

If you are interested in knocking this out early for some sort of community challenge or achievement streak just and have just started the game you can do so in Mission one. Use Coqui to spam it on a group of enemies and then trigger a healing station which will make the cooldown go by much faster OR reload a checkpoint to get the cooldown back immediately and have the previous hits carry over. It takes about 10 to 15 minutes to do this.