How to Make It
Stir together achiote powder, cumin seeds, oregano, cloves, allspice, and peppercorns in a small skillet. Cook over medium, stirring occasionally, until fragrant, about 2 minutes.
Transfer spices to a blender, and process on low speed until coarsely ground, 1 to 2 minutes. Increase speed to high, and process until finely ground, about 40 seconds. Add orange juice, vinegar, garlic, and salt; process until smooth, about 30 seconds, stopping to scrape down sides as needed.
Pat cod fillets dry with paper towels; arrange in a single layer in a baking dish. Pour marinade over fish. Cover and refrigerate 8 hours or overnight.
Preheat oven to 400°F. Remove fish from refrigerator, and bring to room temperature. Using scissors, remove stiff edge of banana leaves, then cut into 14- x 8-inch rectangles. Wipe both sides of banana leaves with a damp kitchen towel to remove any dirt. Using tongs, hold each leaf a few inches over a gas flame, turning leaf often, until softened and aromatic, about 3 minutes. (The leaves will darken as they wilt.) Alternatively, soak the banana leaves in very hot tap water until pliable, about 10 minutes.
Wipe off excess marinade from fish; season both sides with additional salt. Place banana leaves, ridged side down, on a flat surface. Place 1 fillet, skin side up, in center of each banana leaf. For each fillet, fold short end of leaf up and over fish, then fold long end up and over to make a small packet around fillet. Arrange packets, seam side down, on a large rimmed baking sheet, and bake in preheated oven until fish is flaky, 15 to 20 minutes.
Using scissors, cut banana leaves from fish. Using a spatula, transfer fish to a serving platter. Discard banana leaves. Top fish with lime slices and Pickled Red Onions. Serve with tortillas and black beans.