PLACE bread slices on baking sheet; spray with nonstick cooking spray. Broil for about 30 seconds or just until lightly toasted. Turn slices over; broil for an additional 30 seconds. Remove from oven.
COMBINE pesto, vinegar and mustard in small bowl; whisk until smooth. Spread 1 teaspoon pesto vinaigrette over 8 bread slices. Top with small piece of lettuce, 2 slices of tomato and 3 slices of egg. Drizzle with 2 teaspoons pesto vinaigrette. Top with remaining bread slices to create sandwiches. Serve any remaining pesto vinaigrette alongside sandwiches.