The Brief: ZOMG is a synonym for "OMG."

DEEP DIVE
The Z in ZOMG does not stand for anything; it simply stylizes OMG. It is used to show emphatic or overwhelming emotions, such as euphoria. It can also be used in response to something cute, as one might use uwu.
ZOMG @NostalgiaBath I found the greatest gif of all time
Also, I want to write an Oral History of @vincentdonofrio's Goren Lean pic.twitter.com/e95aIJmbtn
— Neil Shurley (@ThatNeilGuy) February 25, 2019
ZOMG! I'm so excited!! π₯³ππβοΈ https://t.co/kXxka1jaL3
— Ian Coldwater π»πΏβ¨ (@IanColdwater) February 25, 2019