Rinse the bacalao fillets in warm water. Boil the fillets in water for 10 minutes. Pour off the water, fill the pot with fresh water and boil for another ten minutes. This is important step to get rid of some of the salt in the bacalao. Or you can simply soak the codfish overnight in a bowl of water.
Drain the water from the fish and flake with a fork. Heat oil in pan, then add onions, pepper.
Sauté for about 2-3 minutes on a medium fire, until the onions are soft. Add tomatoes and pepper and cook for about 10 minutes or until the tomatoes begin to break down.
Add flaked bacalao cook for an additional 10 mins. Add ackee and stir, breaking into smaller pieces.
Cook for an additional 5 minutes or until ackee is warmed and tender, remove from heat. Sprinkle with scallion. Serve warm.