def slurper = new groovy.json.JsonSlurper()
def json = slurper.parseText(myjson)
result = [:]

 json.each {
 result.put(json.menu.items.id,json.menu.items.label)

 }

println result
​

{
   "menu":{
      "header":"SVG Viewer",
      "items":[
         {
            "id":"Open"
         },
         {
            "id":"OpenNew",
            "label":"Open New"
         },
         null,
         {
            "id":"ZoomIn",
            "label":"Zoom In"
         },
         {
            "id":"ZoomOut",
            "label":"Zoom Out"
         },
         {
            "id":"OriginalView",
            "label":"Original View"
         },
         null,
         {
            "id":"Quality"
         },
         {
            "id":"Pause"
         },
         {
            "id":"Mute"
         },
         null,
         {
            "id":"Find",
            "label":"Find..."
         },
         {
            "id":"FindAgain",
            "label":"Find Again"
         },
         {
            "id":"Copy"
         },
         {
            "id":"CopyAgain",
            "label":"Copy Again"
         },
         {
            "id":"CopySVG",
            "label":"Copy SVG"
         },
         {
            "id":"ViewSVG",
            "label":"View SVG"
         },
         {
            "id":"ViewSource",
            "label":"View Source"
         },
         {
            "id":"SaveAs",
            "label":"Save As"
         },
         null,
         {
            "id":"Help"
         },
         {
            "id":"About",
            "label":"About Adobe CVG Viewer..."
         }
      ]
   }
}