Boil the eggs: Place in a saucepan, cover with cold water, bring to a boil, then remove from heat. Cover for 12 minutes, then transfer to ice water.
Peel and chop or mash the eggs to your preferred texture.
In a bowl, whisk mayonnaise, Dijon mustard, lemon juice, salt, and pepper.
Fold in the eggs, chives, and dill until well coated.
Spread on bread slices and serve immediately, or refrigerate filling for up to 4 days.
