[{"data":[{"entry":{"fieldA":"aaa","fieldB":"xxx"}},{"entry":{"fieldA":"ccc","fieldB":"yyy"}},{"entry":{"fieldA":"eee","fieldB":"nnn"}}]},{"data":[{"entry":{"fieldA":"bbb","fieldB":"xxx"}},{"entry":{"fieldA":"ccc","fieldB":"yyy"}},{"entry":{"fieldA":"eee","fieldB":"xxx"}}]}]

db.collection.aggregate([{$unwind:{path:"$data"}},{$match:{$or:[{"data.entry.fieldA":"aaa"},{"data.entry.fieldA":"eee"}]}},{$group:{_id:"$_id",data:{$push:{fieldA:"$data.entry.fieldA",fieldB:"$data.entry.fieldB"}}}}])