Thaw fish and shrimp, if frozen. Rinse; pat dry with paper towels. Place shrimp in a small bowl. Sprinkle half of the Cajun seasoning evenly over fish; rub in with your fingers. Sprinkle remaining seasoning over shrimp; toss to coat. Thread shrimp onto 10- to 12-inch metal skewers, leaving a 1/4-inch space between pieces.
Lightly grease or coat with nonstick cooking spray an unheated grill rack. For a charcoal grill, grill fish on the greased rack of an uncovered grill directly over medium coals for 4 to 6 minutes per 1/2-inch thickness of fish or until fish flakes easily when tested with a fork, turning once. Grill shrimp for 5 to 8 minutes or until shrimp turn opaque, turning once. (For a gas grill, preheat grill. Reduce heat to medium. Place shrimp skewers and fish fillets on greased grill rack over heat. Cover and grill as above.) When done, flake fish into bite-size pieces; remove shrimp from skewers.
Meanwhile, in a large saucepan stir together the broth, lime peel, lime juice, soy sauce, and, if desired, hot pepper sauce. Bring to boiling; reduce heat. Stir in fish, shrimp, green onions, and cilantro; heat through.
To serve, ladle soup into bowls and garnish with mango. Makes 4 servings.