How to render ZF2 view within JSON response?

Answer

public function indexAction()
{
if (!$this->getRequest()->isXmlHttpRequest()) {
return array();
}

$htmlViewPart = new ViewModel();
$htmlViewPart->setTerminal(true)
->setTemplate('model/controller/action')
->setVariables(array(
'key' => 'value'
));

$htmlOutput = $this->getServiceLocator()
->get('viewrenderer')
->render($htmlViewPart);

$jsonModel = new JsonModel();
$jsonModel->setVariables(array(
'html' => $htmlOutput,
'jsonVar1' => 'jsonVal2',
'jsonArray' => array(1,2,3,4,5,6)
));

return $jsonModel;
}

Now, we will grab the view renderer with all the template mapping intact and simply render the ViewModel directly. The only important factor is that you need to specify the fully qualified template to render (e.g.: "$module/$controller/$action")
Response looks like this:
Object:
html: "<h1>Hello World</h1>"
jsonArray: Array[6]
jsonVar1: "jsonVal2"