In a medium bowl, combine the cornstarch, all-purpose flour, salt, and black pepper.
Dip each chicken piece first into the beaten eggs, then coat evenly with the cornstarch and flour mixture. Set aside on a plate.
Heat the vegetable oil in a large skillet or wok over medium-high heat until hot but not smoking.
Fry the chicken pieces in batches for about 4-5 minutes each, turning occasionally, until golden brown and cooked through. Remove and drain on paper towels.
In a separate bowl, whisk together pineapple juice, rice vinegar, granulated sugar, ketchup, and soy sauce until sugar dissolves.
In a small bowl, mix the cornstarch and water to create a slurry.
In the same skillet or wok, add the red bell pepper, green bell pepper, and onion. Stir-fry for 3-4 minutes until slightly tender but still crisp.
Pour the pineapple juice mixture into the skillet with the vegetables and bring to a simmer over medium heat.
Stir in the cornstarch slurry and cook for 1-2 minutes until the sauce thickens.
Add the pineapple chunks and fried chicken pieces to the skillet. Toss gently to coat everything evenly with the sauce.
Cook for another 2 minutes to heat through.
Serve hot over steamed white rice or noodles.