Allah mentioned them only once in the qur'an:
Indeed, those who have believed and those who were Jews and the Sabeans and the Christians and the Magians and those who associated with Allah - Allah will judge between them on the Day of Resurrection. Indeed Allah is, over all things, Witness. (22:17)
This verse can't be used as a clear evidence for considering the Magians or Zoroastrians المجوس as among the people of the book (ahl-al-Kitab) as it quotes them as an example of among those who at least had flaws in their belief as they are taken among the opposite examples to the (right or good) believers.
While Allah quoted the three first of these non-Muslim groups among the believers elsewhere:
Indeed, those who believed and those who were Jews or Christians or Sabeans [before Prophet Muhammad] - those [among them] who believed in Allah and the Last Day and did righteousness - will have their reward with their Lord, and no fear will there be concerning them, nor will they grieve. (2:62)
Which he didn't explicitly for the Zoroastrians.
These both evidences created a certain conflict and a big doubt, on whether or not the Zoroastrians are ahl-al-Kitab! There's as far as I know a consensus among -at least sunni scholars- that it is not allowed to marry their women nor eat from their slaughtered animals.