[majewsky]

Well, you can't. The terminal translates Ctrl-Z into SIGTSTP before it even reaches vim. Alternative suggestion:

  nmap gz :term zsh<CR>

Same number of keystrokes, and does not override any existing normal-mode command from what I can see.

[Pete_D]

    :nnoremap <C-z> :term<Return>

works for me (tmux in urxvt).

Ctrl-Z only gets converted to SIGTSTP if the terminal has ISIG set. For example, try `stty -isig; sleep 5` and try to suspend or interrupt the sleep command.