This is the creation of the UserRegisterListener factory and of its Listener in Zend Framework 2

module.config.php

 'factories' => array(
                'Base\Listeners\UserRegisterListener' => function($sm){
                	$config = $sm->get('config');
                    $config = $config['db'];
                    $dbAdapter = new Zend\Db\Adapter\Adapter($config);
                	$regListener = new Base\Listeners\UserRegisterListener();
                	$regListener->setAdapter($dbAdapter);
        			return $regListener;
		        },

Module.php

<?php

class Module
{
    public function onBootstrap(MvcEvent $e)
    {
        $eventManager        = $e->getApplication()->getEventManager();
        $moduleRouteListener = new ModuleRouteListener();
        $moduleRouteListener->attach($eventManager);
        $adapter = $e->getApplication()->getServiceManager()->get('Zend\Db\Adapter\Adapter');
        $sm = $e->getApplication()->getServiceManager();

        $eventManager->attach(new UserRegisterListener($adapter));  // <<<< here the registration of the listener!!
        
?>

UserRegisterListener.php

<?php
namespace Base\Listeners;

use Zend\EventManager\EventManagerInterface;
use Zend\EventManager\ListenerAggregateInterface;
use \BjyProfiler\Db\Adapter\ProfilingAdapter;

class UserRegisterListener implements ListenerAggregateInterface
{
    protected $adapter;
    /**
     * @var \Zend\Stdlib\CallbackHandler[]
     */
    protected $listeners = array();
    
    public function __construct(ProfilingAdapter $adapter){
    	$this->adapter = $adapter;
    }
   
    /**
     * {@inheritDoc}
     */
    public function attach(EventManagerInterface $events)
    {
        $sharedEvents      = $events->getSharedManager();
        $this->listeners[] = $sharedEvents->attach('ZfcUser\Service\User', 'register.post', array($this, 'onRegister'), 100);
        $this->listeners[] = $sharedEvents->attach('ScnSocialAuth\Authentication\Adapter\HybridAuth', 'registerViaProvider.post', array($this, 'onRegister'), 100);
    }

    public function detach(EventManagerInterface $events)
    {
        foreach ($this->listeners as $index => $listener) {
            if ($events->detach($listener)) {
                unset($this->listeners[$index]);
            }
        }
    }

    public function onRegister($e)
    {
        $user = $e->getParam('user');
        if(!empty($user)){
            $id = $user->getId();
            if(!empty($id) && is_numeric($id)){
                $this->adapter->query('INSERT INTO user_role_linker (user_id, role_id) VALUES (' . $id . ', 2)', \Zend\Db\Adapter\Adapter::QUERY_MODE_EXECUTE);
                return true;
            }
        }
        
        return false;
    }
}