Prestashop module open headless page

In my modules config page (backoffice) I want to open Smarty template file, but it should load just tpl content (no Prestashop header, menu etc).

class MyModule extends Module
{

  public function getContent()
  {
    if (Tools::getValue('customAction') === 'displayMyPage') 
    {
       return $this->displayMyPage();
    }

    $url = $this->context->link->getAdminLink('AdminModules', true, 
    array('configure' => $this->name, 'customAction' => 'displayMyPage'));

    return '<a href="'.$url.'" class="btn btn-danger">Open MyPage</a>';
  }

  public function displayMyPage() 
  {
    $templateURI = __DIR__.'/views/templates/admin/myPage.tpl';
    $output = $this->context->smarty->fetch($templateURI);
  }

}

I tried $this->content_only = true but no luck.

Bit medieval solution but works:

    class MyModule extends Module
    {

     /***
     ***/
    
      public function displayMyPage() 
      {
        $templateURI = __DIR__.'/views/templates/admin/myPage.tpl';
        $output = $this->context->smarty->fetch($templateURI);

        // solution: echo and exit
        echo $output;
        exit;
      }
    
    }