How to return JsonModel by default in ZF2?

Default ViewModel is not mandatory, I can return from controller just the array of data:

public function someAction()
{
  //...
  return array('result'=>$data);
}

But I can`t use this approach with Json. What should I do in dispatch event to wrap the results in JsonModel (for the appropriate accept header)?

Just create Base Controller for all your API controllers, and replace model in MvcEvent.

class JsonRestController extends AbstractRestfulController
{

    public function onDispatch(MvcEvent $e)
    {
        $e->setViewModel(new JsonModel());
        return parent::onDispatch($e);
    }
}