Combine miso paste, mirin, sake, and sugar to make a glaze. Brush the glaze over the black cod fillets and broil for 6-8 minutes until caramelized.
Mix diced oranges, grapefruits, red onions, cilantro, and lime juice to make a refreshing salsa. Serve it over grilled black cod fillets.
Whisk together soy sauce, honey, sesame oil, and minced garlic. Brush the glaze over the black cod and bake it in the oven until cooked through.