PHP theme function to return list of pages with specific template

public static function getParishes()
{
        $collection = new Collection();
        $collection = $collection->ofType('parish')->order('date', 'desc');
        //dump($collection);
        $titles = [];

        foreach ($collection as $page) {
            $titles[$page->slug()] = $page->title();
        }
        return $titles;
}

class Incubator extends Theme
{
    // Access plugin events in this class

    public static function getDioceses()
        {
            $page = Grav::instance()['page'];
            $collections = $page->evaluate(['@root.descendants'])->ofType('parish');
            $titles = [];
            foreach ($collections as $k=>$v) {
                $titles[$v->slug()] = $v->title();
            }
            return $titles;
        }
}