First, you need to season the fish with salt. After that, add some oil in the frying pan and fry the fish until it is entirely brown from both sides.
Take another saucepan and add some oil to it. Saute bell peppers, onion, carrots, ginger and garlic in it. After you saute them for about 3-4 minutes, add some vinegar and cornstarch to it.
After adding the two, stir it and add sugar and ketchup to the pan. Season with some salt and pepper. This will enhance the taste and keep stirring.
Now, all you have to do is, pour the sauce that you made into the fish. Serve it immediately