1 1/2 pounds chicken breasts or pork tenderloin, cut into 1/2-inch to 1-inch pieces
1 each green and red bell pepper, seeded and cut into 1/2-inch pieces
2 cups pineapple chunks (optional)
peanut oil, for frying
For the marinade
2 tablespoons soy sauce
1 tablespoon rice vinegar
1/2 teaspoon cornstarch
For the frying batter
1/2 cup all-purpose flour
1/2 cup cornstarch
1 teaspoon kosher salt
1/2 teaspoon baking soda
2 egg whites
2 tablespoons canola oil
1/3 cup (5 tablespoons) warm water
For the sweet and sour sauce
1/2 cup rice vinegar
1/4 cup plus 2 tablespoons brown sugar
1/4 cup ketchup
1/4 cup pineapple juice
1 tablespoon cornstarch, dissolved in 1 tablespoon water
1/2 teaspoon soy sauce