<select> エレメントを生成するfind('list')を使う際に、出力する値を配列にしたい場合。

キー/値のペア出力

SampleController.php

$query = $articles->find('list', [
    'keyField' => 'slug',
    'valueField' => 'title'
]);
$data = $query->toArray();

参考:https://book.cakephp.org/3/ja/orm/retrieving-data-and-resultsets.html

キー/値(配列)のペア出力

SampleController.php

$query = $articles->find('list', [
     'keyField' => 'slug',
     'valueField' => function ($entity){
                       return [
                          'id' => $entity->id,
                          'title' => $entity->title,
                        ];}
]);
$data = $query->toArray();