I can't say I know much about Zoroasterianism except they believed in one God and were tolerant. I did read that the 3 wise men who brought gifts to Jesus were Zoroasterians --- is that true? It seems that the religion might have been pretty much destroyed by Islam but may have left some influences on the Persians and Turks which is why they seem a little more open and tolerant as a whole than Saudis and the Arabs.
I heard that they were Chaldean priests, who practiced astrology in Iran.
In the past, Zorastrians were identified by Christians as Manicheans, or followers of other gnostic sects, and wiped out in the Byzantine Empire. Within the Islamic empire they were sometimes seen as infidels, but sometimes tolerated as the "Sabeans" star worshippers mentioned with approval in the Koran.
Zorastrians were not passive before the threat of Islamic expansion, and fought back very strongly. They were responsible for the biggest crisis in medieval Islam.
In 928, the 1,500 anniversary of the death of Zoraster, and an astrological event where Saturn and Jupiter appeared together, were taken as predicitions from old Persian prophecies that their day had come. A vigourous Zorastrian sect, the Qarmatians, attacked Arabia itself, got all the way to Mecca, wrecked the Kaba, and took away the famous black stone (a meteorite which adornes the holy house in Mecca.)
They took the black stone to Bahrain. Without it, the Kaba was not complete, and Muslim prayer rituals quite disrupted. Also, according to Koranic beliefs, none of this should have been possible.
A young Persian prince took over the rule of Bahrain, abolished Islamic law, and reinstituted the sacred fires of Zoroastrianism. He announced himself to be the "Twelfth Imam" (the Islamic messiah, awaited by the Shiahs.)
This should have been a high point for the Zorastrians, but instead it was the death knell. After only 80 days, the self appointed Mahdi was killed, and the Arabs took the stone back to Mecca, from whence it has not departed. Zorastrianism went into a decline.