[{"_id":1,"title":"Item-001","tags":["red"]},{"_id":2,"title":"Item-002","tags":["red,yellow"]}]

db.collection.aggregate([{"$match":{"$expr":{"$gt":[{"$size":{"$filter":{"input":"$tags","cond":{"$regexMatch":{"input":"$$this","regex":"red"}}}}},0]}}}])