Here is the full list of all 12 I, Zombie achievements worth 1,000 gamerscore. It takes around 2-3 hours to unlock all of the achievements on Xbox One.
Finish all winter levels
Collect 60 stars
Finish all summer levels
Collect 40 stars
Collect 20 stars
Turn 10 soldiers into zombies
Die for the very first time
Lose a zombie
Turn a human into zombie
Beat all summer levels with total time lower than 15 minutes
Beat all winter levels with total time lower than 8 minutes
Collect 90 stars