pushover vs piece of cake

pushover and piece of cake both are nouns.

Word	Noun	Adjective	Verb	Adverb
pushover	Yes	No	No	No
piece of cake	Yes	No	No	No

As nouns, pushover and piece of cake are synonyms defined as:

Other synonyms of pushover include breeze, child's play, cinch, duck soup, picnic, snap, walkover.

pushover (noun)	piece of cake (noun)
any undertaking that is easy to do	any undertaking that is easy to do
someone who is easily taken advantage of