with one hand tied behind back

with one hand tied behind (one's) back

Easily or effortlessly; encountering no difficulty or resistance (while doing something). I'm a professional musician, so that song is hardly a challenge—I could play it with one hand tied behind my back! Are you kidding? Montgomery is a powerhouse boxer. He'd knock that kid out with both hands tied behind his back!
See also: back, behind, hand, one, tie
Farlex Dictionary of Idioms.

with one hand tied behind one's back

 and with both hands tied behind one's back
Fig. even if under a handicap; easily. I could put an end to this argument with one hand tied behind my back. John could do this job with both hands tied behind his back.
See also: back, behind, hand, one, tie
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • do something with one hand behind your back
  • with one hand behind your back
  • with one hand tied behind (one's) back
  • with one hand tied behind your back
  • could (do something) with one arm tied behind (one's) back
  • with one arm tied behind (one's) back
  • with one arm tied behind one's back
  • with both hands tied behind (one's) back
  • with an arm tied behind (one's) back
  • cakewalk