In a large resealable plastic bag, mix 3 tablespoons pimenta moida, 1/4 cup cider vinegar, 1/2 teaspoon salt, 1/3 teaspoon pepper, 1 tablespoon garlic powder, and 2 tablespoons hot paprika. Place tuna steaks in the bag, seal, and gently shake to coat. Marinate in the refrigerator 1 1/2 to 3 hours.
Melt the butter and heat the olive oil in a large, heavy cast iron skillet over medium-high heat. Discard marinade, and place tuna steaks in the skillet. Fry 2 1/2 minutes on each side, or until fish is easily flaked with a fork. Remove from skillet and drain on paper towels.
Mix 1/4 cup pimenta moida, ketchup, 1/4 cup cider vinegar, water, 2 tablespoons hot paprika, 1/2 teaspoon salt, 1/3 teaspoon pepper, and 1 tablespoon garlic powder into the skillet. Scrape up browned bits, and cook sauce 3 minutes, or until slightly thickened. Scoop a portion of the sauce over the cooked fish to serve, and serve remaining sauce as a gravy for rice and potatoes.
