Using SPL ParentIterator applied on initial RecursiveDirectoryIterator we prepare here iteration only over root subdirectories. With RecursiveIteratorIterator it is possible to use simple iteration by means of 'foreach' command.

$path = "/projects/joomla/components/jot";

$iterator = new RecursiveDirectoryIterator($path, RecursiveDirectoryIterator::KEY_AS_PATHNAME);

$dirsOnly = new ParentIterator($iterator);

$objects = new RecursiveIteratorIterator($dirsOnly, RecursiveIteratorIterator::CHILD_FIRST);

foreach ($objects as $name => $object) {

  $files = glob($name . "/index.html");

  if (count($files) === 0) {

               echo "$name\n";

  }

}