Got it working! 🍎

frontend/models/MealForm.php

@@ -0,0 +1,41 @@
+<?php
+
+namespace frontend\models;
+
+use Ramsey\Uuid\Uuid;
+use Yii;
+use yii\base\Model;
+use yii\web\UploadedFile;
+
+class MealForm extends Model
+{
+
+    /**
+     * @var UploadedFile
+     */
+    public $picture;
+    public string $filepath;
+
+    public function rules() {
+        return [
+            [['picture'], 'file', 'skipOnEmpty' => false],
+            [['picture'], 'required'],
+        ];
+    }
+
+    public function newFileName()
+    {
+        $this->filepath = (string)'uploads/' . Yii::$app->user->id . '-' . Uuid::uuid4() . '.' . $this->picture->extension;
+    }
+
+    public function upload()
+    {
+        if ($this->validate()) {
+            $this->newFileName();
+            $this->picture->saveAs($this->filepath);
+            return true;
+        } else {
+            return false;
+        }
+    }
+}