Cook pasta according to package directions. Drain pasta, rinse with cold water; drain again. Transfer to bowl. Add black beans, chicken, sweet pepper, and red onion; set aside.
Finely shred enough peel of the orange to get 1-1/2 teaspoons. Place shredded peel in bowl; stir in sour cream, salt, and pepper. Juice orange. Add 3 tablespoons orange juice to sour cream mixture.
Add sour cream mixture to pasta mixture; toss to coat. Cover; refrigerate 2 to 24 hours. Before serving, stir in enough milk (1 to 2 tablespoons) until salad is desired consistency. Stir in arugula and cilantro. Makes 4 servings.