Rinse the cod with cold water, then place in a large bowl. Cover with cold water. Cover bowl with plastic wrap or foil and chill at least 24 hours in the fridge, changing the water once. Drain. Place the fish in a large skillet, cover with cold water and bring to a boil. Reduce heat and simmer till fish flakes easily, about 50 minutes. Drain; cool slightly. Using fingers shred the fish, discarding skin and bones. Measure 1 1/2 cups shredded fish and place in a bowl (reserving any remaining fish for another use). Add onion, green bell pepper, tomatoes, lime juice, lime peel, and chile to the fish and stir to blend and season with salt and pepper. The salad can be made up to 4 hours ahead of serving time, covered and chilled. Mound salad in the center of a nice platter. Sprinkle with chopped boiled egg. Surround with the avocado slices and serve.