In this context 'the cucumber job' would refer to a dish or table decoration using cucumber. Used like this, 'job' is slang for something the caterer has been asked to make using cucumber. The word 'job' is often used like this in English informal speech. For example, if a bakery needs to deliver bread rolls to one client and tarts to another, the boss might say: "If you do the bread roll job, someone else can do the tart job.