The phrase "with one hand tied behind one's back" is commonly used to express the ease with which a task can be accomplished. However, there are several synonyms that can be used to convey a similar meaning. For instance, the phrase "a walk in the park" can be used to indicate that a task is easy or effortless. Other synonyms include "child's play," "a cinch," "a piece of cake," "a breeze," and "a snap." These synonyms are useful when emphasizing the simplicity of a task or highlighting the skill level of an individual who can accomplish it with ease.