In a separate bowl, combine 1/2 cup of all – purpose flour, 1/2 cup of cornstarch, 1 egg, 1/2 cup of water, and a pinch of salt. Stir well until a smooth batter forms. The consistency should be thick enough to coat the pork evenly.
Dip each pork strip into the batter, ensuring it’s fully coated.
Heat about 2 inches of oil in a deep pan or wok over medium – high heat. When the oil reaches 160 – 170°C (you can test by dropping a small bit of batter; it should sizzle and float), carefully add the coated pork strips to the oil. Fry in batches to avoid overcrowding. Fry for 3 – 4 minutes until the pork turns light golden – brown. Remove the pork with a slotted spoon and place it on a plate lined with kitchen paper to drain excess oil.
Increase the heat to high and re – fry the pork strips for 1 – 2 minutes until they turn a deep golden – brown and become extra crispy. Remove and drain again.
In a bowl, whisk together 2 tablespoons of ketchup, 2 tablespoons of rice vinegar, 1 tablespoon of sugar, 1 tablespoon of light soy sauce, 1/2 teaspoon of salt, and 1/2 cup of water.
Add 1 tablespoon of cornstarch to the sauce mixture and stir until well – combined.
Pour out most of the oil from the wok, leaving about 1 tablespoon. Heat the remaining oil over medium heat.
Add the onion chunks to the wok and stir – fry for 1 minute until they start to become translucent.
Add the green and red bell pepper chunks and continue to stir – fry for another 1 – 2 minutes until they are slightly softened.
Pour the prepared sweet and sour sauce into the wok. Stir constantly until the sauce thickens and starts to bubble.
Add the fried pork strips to the wok. Toss the pork in the sauce to ensure it’s evenly coated.