Break the cod fish into pieces and place in a saucepan. Fill with enough water to cover. Bring to a boil and cook for 5 minutes. Drain and rinse under cool water. If you want it less salty, repeat the boiling process a few more times. Remove any bones and skin if there are any. Shred the fish into small pieces and set aside in a medium bowl.
Add the tomato and spring onion to the cod. Combine the flour, baking powder and pepper; stir into the cod. Pour in the water and stir just until everything is blended.
Heat 1/4 inch of oil in a large heavy frypan over medium heat. When the oil is hot, drop rounded spoonfuls of batter into the frypan. Fry on each side until golden brown and crisp, about 5 minutes per side. Drain on paper towels and serve hot.