easy peasy (lemon squeezy)

Etymology:

• Easy peasy lemon squeezy is an elaboration on easy-peasy, likewise meaning “extremely easy or simple.” One of the earliest documented instances of easy-peasy appears in the 1940 American film The Long Voyage Home, used to advise a character to handle a suspicious box with care. The film takes place on a British steamship, a setting that accords with the Oxford English Dictionary’s estimation that easy-peasy originates as a British colloquialism or children’s slang.
• The peasy in easy-peasy is an instance of rhyming reduplication, a term best illustrated with some of English’s many other examples: freaky-deaky, razzle-dazzle, super-duper, teenie-weenie, to name a mere few.
• As for lemon squeezy? The origin of this vivid part of the expression is the subject of much speculation. It’s popularly said that easy peasy lemon squeezy comes from a 1950–60s commercial slogan for a British dish soap called Sqezy, which was lemon-scented and packaged in a squeeze bottle. But while there was a product called Sqezy (pronounced like squeezy), there is currently no firm evidence the brand ever used easy peasy lemon squeezy as a catchphrase. Also alluding to the detergent, another theory anecdotally claims the expression goes back to a racially charged British schoolyard chant, “Easy, peasy, Japanesey. Wash your bum in lemon Sqezy.”
• Easy peasy Japanesey points to other elaborations on easy-peasy such as easy peasy pumpkin peasy and easy, peasy weasy, the latter used a 1973 British short story, nearly 20 years before the OED cites easy peasy lemon squeezy, in a 1990 article in the Independent.
• While its exact origins are unknown, easy peasy lemon squeezy has been featured prominently in some popular media, including the 2002 British-parodying comedy, Austin Powers in Goldmember. And in the hit television series The Walking Dead, the brutal villain Negan notably utters the expression after offing a zombie—making the sweet and innocent expression sound very sinister. Source: https://www.dictionary.com/e/slang/easy-peasy-lemon-squeezy/