If you translate it literally, then you get “to tell salads”. Raconter des salades means “to tell stories” or “to lie”. It has been used since the end of the 19th century. It makes sense, as a salad can be a marriage of ingredients that harmonize to give an agreeable blend to savor. If you want to tell an easy to swallow lie, you will have to use a convincing tone and combine humor, false excuses and imagination!