So I've been interested in Zoroastrianism for a while, and I've always thought that part of why it was supplanted by Islam is because Islam is a "missionary" religion, while Zoroastrianism was more of a regional religion. There's other factors of course, but isn't it true that Islam's ability to adapt to other regions than it's religious capital helped it thrive?
So I would like to see a PoD making Zoroastrians into proselytes, and have them expand their religion past Persia. How would this be arranged?