[{"id":1,"data":[{"val1":"xyz","val2":"abc"},{"val1":"a","val2":"b"}]},{"id":2,"data":[{"val1":"d","val2":"e"},{"val1":"f","val2":"f"}]},]

db.collection.find({$expr:{$and:[{$eq:["$data.0.val1","xyz"]},{$eq:["$data.0.val2","abc"]}]}})