1. Combine first 7 ingredients in a bowl.
2. Combine mustard and next 3 ingredients (through honey); stir with a whisk.
3. Spread 2 tablespoons cheese mixture over each bread slice. Top each with 2 lettuce halves, 2 ounces salmon, 4 tomato slices, and 4 cucumber slices. Drizzle each sandwich with 2 teaspoons mustard mixture; sprinkle with 2 tablespoons egg whites. Garnish with dill sprigs, if desired.