What is the ruling on eating food cooked by a Christian chef working in a company in the desert where all the employees are Muslims?

The crucial factor for the permissibility of slaughtered animals is the slaughtering (dhakāh) and the person performing it. If the slaughterer is a Muslim or a person of the Book (Christian or Jew), then it is permissible to eat what they have slaughtered, regardless of the cook's religion. However, if the slaughterer is neither of these, then it is not permissible to eat from what they have slaughtered. As for non-slaughtered items like fish, vegetables, and baked goods, there is absolutely no objection to eating them as long as they are permissible. For slaughtered animals, it is a condition that they are slaughtered according to Islamic law (dhakāh shar‘iyyah) and that they have not been consecrated to other than Allah.