Pour boiling water over the tomatoes to make them easier to peel. Peel and dice tomatoes.
In a saucepan, heat the vegetable oil and add the onion. Fry a few minutes until transparent. Add the carrot and cook a few minutes more. Add the fish, fry for a minute then add the tomatoes.
Add water and bring to a simmer then add potatoes. Season with salt and pepper to taste and cook about 10 minutes, until potatoes are tender.