How to Make It
Soak dried chiles in warm water in a medium bowl until rehydrated, about 10 minutes. Drain chiles; remove and discard chile stems and seeds. Combine chiles, achiote, orange juice, vinegar, garlic, salt, and pepper in a blender. Blend until smooth. Place fish in a ziplock plastic bag. Add sauce, seal bag, and let marinate in refrigerator 2 to 4 hours.
Preheat oven to 375°F. Coat bottom of a 13- x 9-inch baking dish with olive oil. Place pineapple slices in a single layer in dish. Place marinated fish and marinade over pineapple. Bake in preheated oven until fish is crispy on edges and sauce has reduced, about 35 minutes. Remove from oven. Using a fork, break fish apart to allow it to soak in sauce. Serve fish (and pineapple, if desired) on warm tortillas; garnish with cilantro, onion, and avocado. Squeeze lime wedges over tacos just before serving.