Is the Old Testament plagiarized from the Zoroastrian scriptures?

Quite simply, no. Many wild theories are thrown about by theologians
looking for something to put into their ThD theses, and this is one of
these ideas. The Zend Avesta is the principle scripture of Zoroastrianism,
the pseudo-monotheistic sun-worshiping religion which began in Persia in
about the seventh century BCE. One principal problem with this theory is
that most of the Old Testament was written long before the Zend Avesta.
The origins of the Zend Avesta are obscure, but the earliest evidence for
its existence comes from about 600 BCE. Assuming that there are parallels
between the Old Testament and the Zend Avesta which require one to
conclude that one borrowed from the other (and this is a big assumption)
the logical implication would be that the Persian scripture borrowed from
the one which preceded it?the Old Testament! The reason theologians are
not attracted to this theory is that it would not provide an interesting
and controversial ThD thesis topic.

Another problem with this theory is that most of the original Zend Avesta
has been completely lost. In fact, it is difficult to prove that Zoroaster
(also known as Zarathustra) himself is even an historical person, as his
origins and even the time of his life are controversial. The Zoroastrians
now rely principally on the Gathas, which are supposed sayings of
Zoroaster. I say supposed sayings of Zoroaster because this book was
written hundreds of years after the Zend Avesta when most of the original
writings had already been lost to posterity. For this reason, it is
difficult to say what was in the Zend Avesta in the first place. This
would make it hard to prove either that the Bible writers borrowed from
the Zoroastrian scripture or vice versa. With little solid evidence in
either direction, much room is left for those who like to speculate and
who make a living out of finding supposed problems with the Bible. You
would do well to be extremely skeptical of such claims. You should look
for some sort of solid evidence to back up the claim that the Bible
writers borrowed from Zoroastrian scripture. To date, I have seen no
reliable evidence to support the claim, but if you find something, I would
request you send the information my way. I will not be holding my breath.

John Oakes, PhD