atom package manager install is not lazy (it always does a fresh install of a package), but with some shell magic you can make it lazy

lazy_apm_install.sh

#!/usr/bin/env bash

apm_lazy_install() {
   for package in $@; do
      apm list | grep $package > /dev/null ||
         apm install $pacakge
   done
}

apm_lazier_install() {
   for package in $@; do
      ls -l ~/.atom/packages | grep $package > /dev/null ||
         apm list | grep $package > /dev/null ||
         apm install $package
   done
}

echo && echo lazy install
time apm_lazy_install \
   atom-beautify atom-handlebars editorconfig emmet file-types language-gherkin \
   language-gitignore language-haml pretty-json seti-syntax seti-ui

echo && echo lazier install
time apm_lazier_install \
   atom-beautify atom-handlebars editorconfig emmet file-types language-gherkin \
   language-gitignore language-haml pretty-json seti-syntax seti-ui

echo && echo 'normal install (ouch)'
time apm install \
   atom-beautify atom-handlebars editorconfig emmet file-types language-gherkin \
   language-gitignore language-haml pretty-json seti-syntax seti-ui

results.txt

lazy install

real	0m5.888s
user	0m5.192s
sys	0m0.717s

lazier install

real	0m0.040s
user	0m0.022s
sys	0m0.029s

normal install (ouch)
Installing atom-beautify to …/.atom/packages ✓
Installing atom-handlebars to …/.atom/packages ✓
Installing editorconfig to …/.atom/packages ✓
Installing emmet to …/.atom/packages ✓
Installing file-types to …/.atom/packages ✓
Installing language-gherkin to …/.atom/packages ✓
Installing language-gitignore to …/.atom/packages ✓
Installing language-haml to …/.atom/packages ✓
Installing pretty-json to …/.atom/packages ✓
Installing seti-syntax to …/.atom/packages ✓
Installing seti-ui to …/.atom/packages ✓

real	0m49.144s
user	0m39.446s
sys	0m16.270s