Mango and Shrimp Wraps

Ingredients

• 1/3 cup low fat sour cream
• 1/3 cup low fat mayonnaise
• 1/4 cup chopped fresh basil
• 2 tbsp chopped fresh chives
• 2 1/4 tsp salt
• 1/4 tsp pepper
• 1 tbsp fresh lemon juice
• 1 1/2 lb large shrimp in shell (16 to 20 per lb), peeled and deveined
• 1 (1-lb) firm-ripe mango, peeled and cut into 1/3-inch cubes
• 4 (10-inch) whole wheat tortillas
• 1 (6-oz) bunch watercress, tough stems discarded