Complementando o post do Simon (eu estava escrevendo ao mesmo tempo que ele =)): segundo um americano do Wordreference,
a piece of cake means that something is easy, not that it's insignificant. "Was the test hard?" "Naah ... (it was a) piece of cake."
How do you do that?' 'It's a piece of cake! Watch!'
(Longman)Sir Terry Wogan slams 'self-important' newsreaders whose job is a 'piece of cake'.
(dailymail.co.uk)Silvana’s new life is a piece of cake
. (sheffieldtelegraph.co.uk)The new software installation was a piece of cake, no problems!
Outras expressões para designar uma “mamata”: breeze
, sendo esse último termo típico do inglês britânico:It was a breeze.
(Oxford)Going down the hill will be a breeze after the long climb up!
(Oxford)The first question is a cinch
. (Oxford)‘How was the exam?' 'Oh, it was a cinch!'
(Longman)The program is a cinch to install.
(Longman)The first year of the course was an absolute doddle.
(Oxford)The machine is a doddle to set up and use.
Você também pode dizer que something is child’s play
:I've cooked for 200 people before now. So, tonight is child's play by comparison.
(Longman)Skiing is child’s play in Austria.
(express.co.uk)When a man’s job is child’s play.