Combine the oregano, cumin, paprika, 2 teaspoons pepper and 1/2 teaspoon salt; rub over fillets. Refrigerate for at least 30 minutes., Meanwhile, in a small bowl, combine the mango, avocado, red onion, cilantro, lime juice and remaining salt and pepper. Chill until serving., In a large cast-iron skillet, cook fillets in oil over medium heat until fish flakes easily with a fork, 5-7 minutes on each side. Serve with salsa.