There are some that prepare these salads before Shabbos to avoid any shailos. If they were not, one should prepare them in the following manner:
Peeling the eggs and onions. The peeling must be done by hand shortly before the meal, and only the necessary amount that may be eaten during that meal may be prepared. - בורר-
The ideal method is to peel them directly over a garbage can to avoid having to move Muktzah. If one did not do so, the peels may be removed directly only if they are repulsive to him/her in their present location.
Mashing/ grating/ slicing. One may mash eggs regularly but may not use a utensil designated for mashing/grating1 . A slicer may be used to slice eggs.
Cutting onions. One may cut up onions shortly before the meal as long as the cut pieces are larger than usual2. טוחן
Oil should be added to the bowl before the eggs, and mixed in a crisscross fashion.3 - לש
Mayonnaise may be added to the salad after the eggs. Mayonnaise should be mixed with crisscross strokes. לש
Salt. Salt should preferably be added after the eggs are mixed with other ingredients or shortly before meal. - מעבד
Removing a shell fragment. One may remove a shell fragment from the egg salad only if some egg salad is removed along with it. - בורר-
Notes: One may pour out the water from a pot of boiled eggs, since eggs in water are not considered a mixture. A hot egg (110°F) may not be placed into cold water nor rinsed with cold water4 .
A scooper may be used to serve egg salad.
Tuna salad: The following guidelines should be followed: The lid of the can should only be opened halfway with a can opener. - מנא תיקון- It is permissible to finely mash the tuna. If oil or mayonnaise will be mixed into the tuna, follow as above in egg salad.
-לש- 1 Eggs are exempt from the prohibition of Tochein, grinding, because in relation to food, the prohibition only applies to foods that grow from the ground. Tuna would be similarly exempted. 2 Since the prohibition of Tochein applies to foods that grow from the ground, which includes onions. 3 Loose mixtures are permitted to be made by changing the order of the ingredients added and the manner in which it is mixed. 4 Even though the water that is actually rinsing the egg will not get cooked, the remaining drops will.
א. שש''כ פ''ח סעי' כ''ח ג. סי' שכ"א סעיף י', אג"מ או"ח ח"ד סי' ע"ד טוחן אות ד'. ה. סי' שכ"א סט"ז. ז. סי' שכ"א ס"ק כ"א.