Here's an excerpt from my routes.php.
$app->get ('/faq', 'App\Controller\UserController:faq')->setName ('guest_faq');
$app->get ('/login', 'App\Controller\UserController:login')->setName ('guest_login');
$app->get ('/logout', 'App\Controller\UserController:logout')->setName ('guest_logout');
In my opinion (and I may not be 100% correct here) this is simple, clear and readable.
Please don't misunderstand: I'm not trying to tell you how to write your code, I'm just trying to give the best advice I know for Slim.