Place 6 large eggs in a pot, cover with water, and add vinegar. Boil until water bubbles, then turn off heat and let sit for 1 hour.

Once cool, peel the eggs gently. Slice each egg in half, separating yolks from whites.

Dice the egg whites and crumble the yolks into a mixing bowl.

Add diced tomatoes, chopped lettuce, sliced green onions, mayonnaise, yellow mustard, and black pepper to the bowl. Mix thoroughly.

Cover the bowl and refrigerate for at least 1 hour.

Optionally, spread a layer of butter or mayonnaise on the chosen bread.

Pile the egg salad mixture generously onto one slice of bread, top with another slice, and press gently to seal.