Mix all the ingredients for Mixture A in a medium bowl and set aside. Taste and adjust seasoning, if necessary.
In a large bowl, add all the ingredients in Mixture B. Mix well and set aside.
Combine all the ingredients for the breading mix (Mixture C) and blend well. You can either use a big bowl, a clean paper bag or a large ziploc bag.
Heat a large frying pan and add oil, about 1 to 1 ½ inches deep. Transfer the chicken pieces to the breading mix and coat each piece completely. Shake off excess flour and transfer to a large tray (like a cookie sheet). Fry the chicken pieces (in batches) until golden brown and crisp, about 4 minutes. Make sure the meat doesn’t touch each other to maintain the oil temperature and not make the chicken oily after frying. Place fried chicken pieces on a cooling rack on top of a cookie sheet or a colander to let the excess oil drip.
Heat another large pan or a wok (medium heat) and add 1 tablespoon of oil. Add the carrots, onion, bell peppers and stir fry for a minute. Next add the pineapple chunks, sweet and sour sauce (Mixture A) and the cornstarch mixture to thicken sauce. Stir to combine and cook for 2 minutes on medium-low heat.
Add the fried chicken pieces and toss for a minute or two, using 2 wooden spoons until all the meat is evenly coated with the sauce. Serve immediately.