I see everyone already jumped on it.
Yes, the Orthodox teaching of theosis is NOTHING like the Mormon belief. Even Athanasius' quote (God became man so that man might become god) is something that people with the wrong idea can easily misunderstand.
The Orthodox Church is clear that God IS God, and that His essence - His "Godness" is something that we will never, ever share in - in fact, we cannot comprehend or experience in truth. We are forever creatures, and He is forever God, and that line will never, ever be crossed or blurred.
A better explanation is that we will be LIKE Him, imo. At least for the Protestant mind, that is a better explanation of what is really meant by "theosis". I'm not claiming to know everything or understand the depths of it, but truly ... we are changed and grow to be more and more in His likeness as Christ is formed within us. There are plenty of Scriptures that attest to this growth of Christ-like-ness, and it is the attainment of that being like Christ that the Orthodox Church teaches.
(Not that there is an "arrival" end point, btw, but there is speaking of having "attained theosis" ... however the teaching is also that we can forever grow in grace and be made more like Him - but we shall never "arrive".)
I hope that makes sense, and forgive me if I made any mis-speak in here - always open to correction - but that should be the Orthodox perspective in its basic form.