Place the eggs in a saucepan and cover with cold water by an inch. Bring to a boil over medium-high heat, then cover, remove from the heat and let stand for 11 minutes.
Transfer the eggs to a bowl of ice water and cool for at least 5 minutes. Peel them under running water.
Chop the eggs into small pieces, or mash them with a fork for a smoother texture.
In a bowl, mix the mayonnaise, yogurt, mustard, lemon juice, salt and pepper.
Fold in the eggs, celery, onion, chives and dill until evenly combined. Taste and adjust the seasoning.
Toast the bread if you like. Layer lettuce on half the slices, spoon the egg salad on top, sprinkle with paprika and close the sandwiches.