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.
輕而易舉, 一隻手被綁在背後也能做
to be able to do something very easily, even under difficult circumstances
:
•
He's so skilled, he could do this job with one hand tied behind his back.
他技術嫻熟,即使一隻手被綁在背後也能完成這項工作。
•
For an experienced chef, making this dish is like doing it with one hand tied behind their back.
對於經驗豐富的廚師來說,做這道菜就像一隻手被綁在背後一樣簡單。