How to make a salad on Shabbos? Or otherwise put what could possibly potentially be wrong with making a nice salad on Shabbos?

After the grain was isolated from the dirt it was ground into flour.

The melacha of grinding is breaking down and reducing a sizable entity into small parts whereby it becomes suitable for a new use.

So, crushing, chopping, pulverizing any object into small particles whether by hand or with a utensil.

Eg chopping lumber into wood chips.

By food, it's only an issue when food is reduced to small particles which makes it easier to eat. 

There are 4 exceptions to grinding under which if you have even 1 of these 4 its ok:

1) It is only an issue with  earth grown foods. So, meat, fish, cheese etc can be chopped up.

2) There is no problem  of grinding after grinding. 

So you could crush a cookie into tiny crumbs because the flour was already ground.

3) For immediate use is fine.

So even if it wasn't pre ground, and it came from the ground you can reduce the fruit or vegetable to a pulverised mass eg by chewing on a carrot.

4) When done in an abnormal way is fine, eg grinding with the handle of a knife is ok.

So, when we speak about making a salad on Shabbos, other than "borer" - sorting issues we saw such as removing bugs or taking the bad from the good, the issue to look out for is grinding related.

The way to deal with this issue is to prepare the salad immediately before consumption. The other exemptions of not growing from the ground and being chopped previously don't apply.

If it's not practical to chop the fruits or vegetables just "before" the meal you can avoid the issue by either using the back of a knife, or by cutting it into long thin slices under which the whole issue doesn't arise.