Marinate prawns with egg, salt and cornflour and then deep fry them and set aside.
In the same wok or pan, remove all the oil and retain only a teaspoon if you like.
Add in the tomato ketchup and red chilli sauce. Stir fry for 30 seconds on medium heat and add salt, sugar and 1/4 cup of cornflour slurry. To make the cornflour slurry, dissolve a teaspoon of cornstarch into 1/4 cup of water.
Add Soy sauce, vinegar and stir on a medium to low flame
Add water, approximately 1/4 cup depending on how thick or thin you want the sauce to be.
Add the cut vegetables and let them simmer in the sweet and sour sauce for 1 to 2 minutes.
Finally, drop in the fried prawn and toss them well in the sauce along with the vegetables till they are well coated and then switch off the flame.
Sweet and Sour Prawns Stir Fry gets done in minutes.