Spiced Mahi-Mahi with Mashed Plantains and Pickled Onion

Name: Spiced Mahi-Mahi with Mashed Plantains and Pickled Onion
Yield: Serves 4
Cuisine: Latin America & Caribbean, Caribbean
Ingredients: 3 , green plantains, peeled, halved lengthwise, and cut into 1-inch pieces; 4 teaspoons, table salt, divided; 3 tablespoons, unsalted butter; 4 (8-ounce) skinless, mahi-mahi fillet, 1 to 1½ inches thick; 2 tablespoons, jerk seasoning; ½ teaspoon, pepper; 2 tablespoons, vegetable oil; 1 recipe, recipe