"Piece of cake" is another expression that means something is extremely easy to do.

VOA: special.2009.06.07

Trivial, smart animal, piece of cake.

对于这么聪明的动物，这易于反掌。

耶鲁公开课 - 心理学导论课程节选

A friend might tell you that his new job was a "piece of cake."

VOA: special.2010.08.29

Unless it is a "piece of cake."

VOA: special.2009.06.07