can zsh do 2 stage completion?

You should explore the compinstall completion customization program.

autoload -Uz compinstall && compinstall

In the version that I am using (zsh 4.3.10), the option for inserting unambiguous prefixes is inside the following menu

• 3 “Styles for changing the way completions are displayed and inserted.”
  • 2 “Change how completions are inserted: …”
    • 1 “… insert any unambiguous prefix rather than [going] straight to menu completion”
      • y

Once saved, this results in the following command saved to the completion customization file (usually .zshrc):

zstyle ':completion:*' insert-unambiguous true

• 3 “Styles for changing the way completions are displayed and inserted.”
  • 3 “Configure … completion lists, selection of items, …”
    • 2 “Use cursor keys to select completions from completion lists.”
      • 1
      • Return

Once saved, this results in the following customization:

zstyle ':completion:*' menu select=1
zstyle ':completion:*' select-prompt %SScrolling active: current selection at %p%s

You might like to customize the first one by adding interactive:

zstyle ':completion:*' menu select=1 interactive