Dear Francis,
FoodBook is a WooCommerce based plugin. Hence, you need to use WooCommerce Product to add a product or menu. Also, all WooCommerce Products will show as a product/menu with FoodBook.
Moreover, all product adding related options (like extra options of a product) included in WooCommerce Product. You will get the option there. https://themelooks.net/documentation/plugin/foodbook/how-to-add-product-extra-items%e2%80%8b/
Best Regards,
ThemeLooks Support Team