A little example:

#!/bin/bash

title="Server Options"
prompt="Pick an option:"
options=("option 1" "option 2" "option 3")

while opt=$(zenity --width 500 --height 300 --title="$title" --text="$prompt" --list --column="Options" "${options[@]}"); do

    case "$opt" in
      "${options[0]}" ) zenity --info --text "option 1";;
      "${options[1]}" ) zenity --info --text "option 2";;
      "${options[2]}" ) zenity --info --text "option 3";;  
    esac

done

Double click an option or click and hit enter does not execute: zenity --info --text "option X" , as it should.

Click an option and hit OK works as expected.