config.js

// config.js
export default {
   view: {
       map: {...},
       widgets: [{
           type: 'layers',
           options: {
               // pass options to the layers list widget
               // https://developers.arcgis.com/javascript/latest/api-reference/esri-widgets-LayerList.html#listItemCreatedFunction
               listItemCreatedFunction(item){
                   item.panel = {content: item.layer.layerId + ' ' + item.layer.title }
               }
           }
       }]
   }
}