someone could do something with one hand tied behind his/her back
US /ˈsʌm.wʌn kʊd duː ˈsʌm.θɪŋ wɪð wʌn hænd taɪd bɪˈhaɪnd hɪz hɜːr bæk/
UK /ˈsʌm.wʌn kʊd duː ˈsʌm.θɪŋ wɪð wʌn hænd taɪd bɪˈhaɪnd hɪz hɜːr bæk/

1.
a occhi chiusi, con una mano legata dietro la schiena
to be able to do something very easily, even under difficult circumstances
:
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He's so skilled, he could do this job with one hand tied behind his back.
È così bravo, potrebbe fare questo lavoro con una mano legata dietro la schiena.
•
For an experienced chef, making this dish is like doing it with one hand tied behind their back.
Per uno chef esperto, preparare questo piatto è come farlo con una mano legata dietro la schiena.