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Separate 1 egg; place egg white in large bowl and place egg yolk in small bowl. Cover and refrigerate egg yolk until needed.
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Add 1 tbsp cornstarch, rice wine, soy sauce and dark soy sauce to egg white; whisk until well combined. Add chicken; stir to coat. Cover and marinate in refrigerator 1 hour.
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Add remaining whole egg to reserved egg yolk; whisk until well combined. Add to marinated chicken; stir to coat. Place remaining cornstarch in separate large bowl. Working in batches, toss chicken in cornstarch to coat. Remove from cornstarch, shaking off excess; transfer to rimmed baking sheet. Once all chicken is coated, return all chicken at once to bowl with cornstarch; toss again to coat. Remove from cornstarch, shaking off excess; return chicken to baking sheet.
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Heat oil in large deep saucepan or deep-fryer until deep-fryer thermometer reads 350°F (180°C) when inserted in oil. Fry chicken in small batches, turning often, until golden all over, 3 to 4 minutes per batch. Transfer to paper towel-lined plate to drain. Set aside.
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Prepare sauce: Heat oil in large non-stick skillet or wok over medium-high heat. Add garlic and ginger; cook, stirring, until fragrant, about 30 seconds. Add red onion, red pepper and green pepper; stir-fry until peppers are tender-crisp, about 2 minutes. Add pineapple; stir-fry until heated through, 1 to 2 minutes.
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Whisk together rice vinegar, brown sugar, ketchup, soy sauce, rice wine, cornstarch and 3/4 cup water in separate small bowl. Add to skillet. Cook, stirring, until sauce is thickened and no longer cloudy, 2 to 3 minutes.
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Add cooked chicken; cook, stirring, until coated, 2 to 3 minutes. Remove from heat; stir in half of the green onions. Transfer to serving dish; sprinkle with remaining green onions.