Alternatives to the passive
Sein plus zu plus infinitive can express necessity or possibility, depending on context. Sich lassen plus infinitive expresses possibility. Both allow the affected thing to be the subject without using werden passive.
Understand the idea
Several active-looking constructions can convey a passive-like meaning. Sein plus zu infinitive often expresses necessity or possibility, while sich lassen plus infinitive commonly presents something as possible or manageable. Their interpretation depends on the surrounding context.
Build it step by step
With sein + zu, the affected thing is the subject and the infinitive carries the action. With sich lassen, conjugate lassen for that subject, add the reflexive pronoun and use a bare infinitive. Adverbs such as leicht help express how easily something can be done. These patterns do not all carry exactly the same nuance as a werden-passive.
See it in a sentence
Der Antrag ist noch zu prüfen.
Die Rechnung ist sofort zu bezahlen.
A useful memory aid
Paraphrase the sentence with must be done or can be done, then check which interpretation the context supports.
A common trap
Do not add zu after lassen in this construction. Also avoid assuming that sein + zu always expresses an obligation; possibility can be the intended meaning.