Database
[{"_id":0,"Client__r":"Total","Module__r.Name":"Oil","Module__r.Reference_Offre__c":"O-AMP-CBA"},{"_id":1,"Client__r":"Total","Module__r":{"Name":"Oil","Reference_Offre__c":"O-AMP-CBA"}}]
Query
db.collection.find({$expr:{$eq:[{$getField:"Module__r.Name"},"Oil"]}})