Place the chicken breast on a cutting board and cut them into small pieces.
1 pound chicken breasts
Pat dry with another paper towel. Patting them dry helps in sticking seasoning on them.
Season with kosher salt and freshly ground black pepper.
Kosher salt, Freshly ground black pepper
Pour 2 quarts oil (or enough to measure about 1½-inches deep) in a large Dutch oven set over medium-high heat. Bring the oil to 350 degrees.
2 quarts peanut or vegetable oil plus 3 tablespoons for the batter
While the oil heats, whisk together flour, cornstarch, baking powder, baking soda, 2 teaspoons kosher salt and 1 teaspoon black pepper in a large mixing bowl. Add the water and the remaining 3 tablespoons oil; whisk until smooth.
Kosher salt, Freshly ground black pepper, 1 cup all-purpose flour, 1 cup cornstarch, 2 teaspoons baking powder, ½ teaspoon baking soda, 1¼ cups water
Place the chicken cubes in the batter and stir to completely coat.
Once the oil reaches 350°F, use a fork to carefully drop each battered chicken cube into the hot oil. (Have a second fork ready to use to release the chicken into the oil, if necessary.)
Food thermometer
Check the oil temperature frequently and adjust the heat, up or down, to keep the temperature between 350-375 degrees F.
Use a spider skimmer to stir the chicken pieces gently to prevent them from sticking together. Cook until chicken is golden, 2-3 minutes each batch. Transfer chicken to paper towel-lined half of the prepared rack.Repeat process until all the battered chicken is fried. Kitchen Spider Skimmer
When all the chicken has been cooked, remove the pan from the heat. Carefully pour all, except 1-2 tablespoons oil, into a heatproof bowl.
Return the Dutch oven to the stovetop set over medium heat. Once the oil is hot, add the red pepper, half the cut scallions, and all the pineapple chunks. Cook 2-3 minutes or until the red pepper is crisp-tender.
2 red bell peppers, 6 scallions, 4 slices fresh pineapple
Add 1-cup sauce to the vegetable mixture and cook until sauce is heated through, about 1 minute.
Add the chicken and stir gently to coat the chicken. Cook just enough to heat the chicken through and serve immediately over cooked white rice and with the remaining sweet and sour sauce.
White rice cooked per package directions.
Garnish with the remaining half of cut scallions.