Place eggs in a heavy-bottomed sauce pan. Add enough cold water to sauce pan to cover eggs plus about 1 inch. Bring water to a rolling boil and then turn off the heat. Pour off all of the hot water from the eggs and replace with cold water. Peel eggs and place in a large bowl.
Using a pastry blender, a fork, or a potato masher, mash eggs.
Add mayonnaise, diced bacon and onion.
Add salt and pepper to taste.
Serve on a sandwich made of buttered and toasted bread or as a salad on a bed of greens or slices of tomato.