Hard-boil the eggs. Remove from the heat. Dip the eggs in cold water and separate the shells.

Place the peeled eggs in a mixing bowl and smash with a fork. Mix chopped onion, mayonnaise, salt and season with freshly ground black pepper.

Now arrange onions and tomatoes slices on sliced bread.

Split the egg mixture on it and arrange sliced cucumber.

Cover it with another bread slice. Cut the sandwich in half to serve.