Hard-boil the eggs, then peel and chop them.

In a bowl, combine chopped eggs, mayonnaise, mustard, celery, red onion, salt, black pepper, and dill if using. Mix well.

Spread the egg salad mixture onto 4 slices of bread.

Add lettuce and sliced tomato on top if desired, then layer with remaining bread slices.

Cut sandwiches in half and serve.