A mix of fresh leaves with, for instance, tomato, onions, beetroot etc. Many earlier receipts (Robert May 1660, Francatelli 1852, Evelyn 1699) include mint leaves, though this is now unusual.

Original Receipt in Evelyn 1699;

A Goodly sallet;
Lettuce, Leeks, Mint, Rocket, Colewort-Tops, with Oyl and Eggs.