Cut the pork into 3/4-inch / 2 cm cubes.
In a large bowl, mix together cornstarch, flour and salt.
Add the egg, 1 tablespoon oil and water. Whisk until smooth. The mixture will be thick like pancake batter.
Add the cubed pork to the mixture and toss to coat.
Heat the oil to 350˚F / 175˚C in a deep-fryer or medium saucepan, and set aside a wire rack.
Add the pork in batches and deep fry for about 5 minutes until golden and crispy.
Remove to the rack with a slotted spoon, and repeat for remaining pork.
Heat a skillet or wok over medium-high heat and add 1 tablespoon oil.
Sauté onion, bell peppers and pineapple in the pan for 2 - 4 minutes until slightly softened.
Add the sugar, vinegar, soy sauce and ketchup. Bring to a simmer.
In a small bowl or teacup, mix together the cornstarch and water to make a slurry.
Slowly stir it into the pan. Simmer for 1-2 minutes or until the sauce is thick enough to coat the vegetables.
Add in the cooked pork and stir to coat evenly with the sauce. Serve and enjoy!