A lot has changed since 2014.
Today you simply do:
# Activate env_parallel function (can be done in .zshenv)
. `which env_parallel.zsh`
function my_func(){ echo $1;}
env_parallel "my_func {}" ::: 1 2
If your environment is big:
# Activate env_parallel function (can be done in .zshenv)
. `which env_parallel.zsh`
# Record which environment to ignore
env_parallel --session
function my_func(){ echo $1;}
env_parallel "my_func {}" ::: 1 2