"Fanya kazi" is imperative
kufanya kazi = to work / working
Fanya kazi! = Work! (imperative to one person)
kazi = work (noun)
I think I've figured this one out now. It's actually an imperative, so "to work" would be an imprecise translation. The best one is in fact simply "work". The word or sentence i was looking for was "kufanya kazi".