Marinate the fish. Cut the cod fillet into pieces, add salt and pepper. Grease with vegetable oil, leave to marinate for 15 minutes.
While the fish is marinating, fry the vegetables. Heat a frying pan with vegetable oil. Fry the onion until golden brown for 1-2 minutes, add the carrots. Simmer for 2-3 minutes until half-ready. Don't forget to stir. Add the tomato, simmer for another 5 minutes. Place the fish pieces on the vegetables, cover with a lid and simmer over low heat for 15 minutes.