A French-inspired Vietnamese sandwich.
Combine carrot, celery, and scallions in a bowl. Pour vinegar over vegetable mixture and toss to coat; set aside to marinate.
Stir cilantro, mayonnaise, yogurt, lime juice, and cayenne pepper together in a bowl. Spread about 2 teaspoons cilantro sauce onto bottom piece of each baguette.
Remove vegetables from vinegar using a slotted spoon, discarding vinegar. Spoon vegetables over cilantro sauce layer on baguette pieces.
Mix prawns in the remaining cilantro sauce and arrange 10 prawns over vegetable layer; top with cucumber slices. Place top piece of baguette over cucumber layer, creating a sandwich.
Per Serving: 388 calories; protein 28.2g; carbohydrates 60.9g; fat 3.3g; cholesterol 148mg; sodium 885.7mg.