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";
}
}