Database
[{"GENUS_DATA":{"File_6489248.ZLM":{"MeterID_6489248":{}}}},{"GENUS_DATA":{"File_12345.ZLM":{"MeterID_12345":{}}}}]
Query
db.collection.aggregate([{$project:{GENUS_DATA:{$objectToArray:"$GENUS_DATA"}}},{$project:{GENUS_DATA:{$map:{input:"$GENUS_DATA",as:"item",in:{"File-Name":"$$item.k",met:{$objectToArray:"$$item.v"}}}}}},{$project:{GENUS_DATA:{$map:{input:"$GENUS_DATA",as:"file",in:{"File-Name":"$$file.File-Name","met":{$map:{input:"$$file.met",as:"met",in:{"METNO":"$$met.k",data:"$$met.v"}}}}}}}}])