%dw 1.0
%output application/json
---
(payload replace /[{}]/ with "" splitBy ";")  map using (data = $ splitBy "=")   {
    (data[0]) : data[1]
}

[
  {
    "key1": "value1"
  },
  {
    "key2": "value2"
  },
  {
    "key3": "value3"
  },
  {
    "keyn": "valuen"
  }
]