[{"_id":1,Email:"testmeals@fsdf.com",Password:"password1",Users:[{Username:"junit",PIN:"9999"}]},{"_id":2,Email:"ddddddd@fsdf.com",Password:"password2",Users:[{Username:"zunit",PIN:"1234"},{Username:"munit",PIN:"8882"}]}]

db.collection.aggregate([{$match:{"Users.Username":"munit"}},{"$project":{_id:false,USER:{$filter:{input:"$Users",as:"users",cond:{$eq:["$$users.Username","munit"]}}}}},{"$unwind":"$USER"},{"$project":{USER_PIN:"$USER.PIN"}}])