def jsonString = """{  "Errors": [],
  "Loans": [ 
    {
      "Applications": [
        {
          "id": 1,
          "name": "test"
        }
      ]
    },
    {
      "Applications": [
        {
          "id": 2,
          "name": "test3"
        },
        {
          "id": 3,
          "name": "test3"
        }
      ]
    }
  ]
}"""

def json = new groovy.json.JsonSlurper().parseText(jsonString)

//To get all loan applications
json.Loans.each {println it}

//The way you want
def getLoanAt = { json.Loans[it] }
println getLoanAt(0)