An employee serves customers in a Chipotle restaurant in Washington, DC on September 9, 2015. Chipotle, the burrito chain whose rocketing growth has fast-food giants like McDonald's reeling, is not slowing down: it plans to hire 4,000 new staff in one go. AFP PHOTO/ ANDREW CABALLERO-REYNOLDS (Photo credit should read Andrew Caballero-Reynolds/AFP/Getty Images)
