What vivid verb should I use when someone "turns into" a zombie?

OED has a first citation from NY Times, 1950 for...

zombify: to transform into a zombie.

...so I don't see why in OP's context he shouldn't say...

"I hope that you're not being/becoming zombified by your love of my brain."

"Mutate" seems appropriate to me.

How about transmogrify?

to change or alter greatly and often with grotesque or humorous effect

I don't think there is anything wrong with saying turn, in this context. See http://dictionary.cambridge.org/dictionary/british/turn_4 , which has the following definition of the word: to (cause to) become, change into, or come to be something. It's good enough for zombie films and television programmes, where characters talk of other people who have turned, meaning that they became a zombie.