Plucked from one of Shakespeare's 15th-century plays, the phrase came to reference the “greenness” of youth, a time of dalliance and frivolity when caution is thrown to the wind. And “salad” in Shakespeare's time broadly referenced far more than lettuce and dressing; it referred to a complex mix of chopped, mixed and seasoned vegetables.
No doubt, restaurateurs today are having great fun with salads as they eagerly tear down the barriers that have narrowly defined the salad as a rather pedestrian mix of lettuce, tomatoes, cucumber, croutons and dressing. Evidence does indeed point to restaurants circling back to what may have been the original concept of the salad as a grab bag of healthful and tasty goodies, rather than a bland, obligatory pre-meal diversion.