To unlock this Achievement, you need to let your team members clear out all the enemies in a single chapter.
You must refrain from pulling the trigger even a single time. If you squeeze it lightly to swing out of cover but don't fire off a round, it will still prevent you from earning the Achievement.
Try this on the Retomoto Tower level. You've got a full-sized crew and there is plenty of cover for you to lay low while directing your crew with the Y button to attack the targets in your sights. Make sure you dart out to administer adrenaline to any fallen comrades when the coast is clear. Once the level has been completed, the Achievement will unlock.
Feel free to drop the game down to Aspirin difficulty level, as it does not affect the Achievement.