Sauce: Mix ketchup, sugar, vinegar. Keep mixing until the sugar will dissolved. Set aside

Coat the Fillet with flour then fry it. Set aside

Stir fry onion until translucent, then add carrot. Add a little water to soften the carrot. Then add in bell pepper and the sauce. Simmer. Lastly add the fish Fillet gently mixing it. Let the Fillet absorbs the sauce. Taste it if the blending of sweet and Sour suits your taste. If not add some more sauce. Serve