Mix cornstarch with pepper, oregano, and salt. Coat the fish with the cornstarch and shake off the excess.Heat the oil over medium heat in a non-stick frying pan.Fry the fish until golden brown on both sides. Set aside.
2. Make the sauce
Heat the olive oil over low heat. Add the onion and cook stirring until it becomes transparent.Add the tomato and chili and cook, stirring for one minute. Add the tomato sauce and water. Cover and cook until the tomato and chili are cooked.Season with salt to taste. Add parsley and mix.
3. Cook
Add the fish and turn to coat with the sauce on both sides.Remove from heat and serve immediately with the lime wedges, see serving ideas above.