Thaw halibut and scallops, if frozen. Cut halibut into 1-inch pieces, and cut large scallops in half or quarters; set aside. In a large saucepan heat oil over medium heat. Add onion, sweet pepper, and garlic; cook about 5 minutes or until tender, stirring occasionally. Stir in tomatoes, vegetable broth, the water, corn, cumin, and ground black pepper. Bring to boiling; reduce heat. Cover and simmer for 10 minutes.
Add halibut and scallops to tomato mixture. Return to boiling; reduce heat. Simmer, uncovered, for 2 to 3 minutes more or until scallops are opaque and halibut flakes easily when tested with a fork.
Stir in clams and cilantro just before serving. If desired, sprinkle with cracked black pepper.