Not that I have any good reason to defend these misguided pagans, but having met a few "(east) Indian-American" Zoroastrians recently, I read this about them:
"Zoroastrianism is the ancient religion of Persia. It was founded about 3500 years ago by the prophet Zarathushtra. Arising out of the polytheistic traditions of ancient India and Iran, he was one of the first monotheists in human history. Zarathushtra preached that there was one God, whom he called Ahura Mazda. Ahura means 'Lord,' and Mazda means 'Wise,' so Zoroastrians call God the 'Wise Lord.' "
Of course, Tolkien's Catholic theological myth structure is "True Myth".
There are two gods. The "Good Spirit" is Ahura Mazda and the "Evil Spirit" is Angra Mainyu. Their relationship to one another is very similar to Yin and Yang.
The portions of the Avesta of Zarathustra which survived Islam's attempt to wipe from the face of the Earth are quite interesting reading. Also - though often considered apocrypha - the Desatir is very beautiful. I suggest them both.