For egg salad, in a medium bowl stir together eggs, pickle relish, mayonnaise, and mustard. If desired, cover and chill for up to 6 hours.
To assemble sandwiches, layer the bottom halves of the croissants with lettuce leaves. Spread egg salad over lettuce. Add top halves of croissants. If necessary, use wooden toothpicks to secure sandwiches. Makes 4 sandwiches.