I think you just need something like this:
PHP Code:
$output["variable"] = vB_Template::create('new_template')->render();
since the eval has been moved in to the vB_Template class. But if the template requires any variables, they now have to be registered. So it's likely you need something like:
PHP Code:
$templater = vB_Template::create('new_template');
$templater->register('var1', $var1);
$templater->register('var2', $var2);
// etc, for each var needed by the template
$output["variable"] = $templater->render();