Q) Is there any issue of losh to prepare a vegetable salad on Shabbos?
A) We find in the Poskim[1] that one of the fundamental principles of meleches losh is that through creating the mixture the various components will bind together and form one entity. However, if the components merely remain mixed together but do not form one entity, this is not included in the prohibition of meleches losh and is subsequently permitted on Shabbos.
Therefore, a vegetable salad that contains pieces of vegetable that are not finely chopped may be prepared on Shabbos, and one can even add salad dressing to such a salad since such a mixture is not included in the prohibition of losh[2].
When discussing “finely chopped” pieces of vegetable in this context, the parameters are not the same as with meleches tochein, where we generally refrain from chopping vegetables into small pieces altogether. However, regarding meleches losh the only issue is to mix together very small pieces; i.e. that the pieces will now be turned into one cohesive mixture by adding liquid[3].
Therefore, a regular vegetable (or fruit) salad may be prepared on Shabbos with salad dressing, and one can even mix the salad in the regular way (i.e. without a shinui) because this is not included in meleches losh.
The only issue would be to use very finely chopped pieces of fruit or vegetables which will form a paste-like mixture when mixed with liquid, such as an olive dip or the like.
[1] משמעות הט”ז שכ”א ס”ק י”ב; משמעות המ”ב שכ”א ס”ק נ’; שש”כ פרק ח’ א’
[2] ט”ז ס”ק י”ב; מ”ב ס”ק ס”ח; אורחות שבת ח”א פרק ו’ כ”ט
[3] אורחות שבת ח”א פרק ו’ הערה ס”ד