Soak black beans in water for 20 minutes; rinse, drain, and mash. In a wok or large skillet, heat the oil to 375°F. Clean and score fish; season with salt and dust with cornstarch. Fry fish for about 6 to 8 minutes or until fish are crisp and golden brown. Drain. In another wok or skillet, heat the butter. Add ginger, garlic, black beans, cilantro, green onion, and red peppers; cook for a few minutes. Add chicken broth, oyster sauce, soy sauce, and sugar; bring to a boil. Combine the 1 1/2 tablespoons cornstarch with the water; add to mixture and cook until thickened. Place fish on a serving platter and top with sauce. Makes 4 servings.