🍗 Prepare the Chicken:
In a shallow bowl, mix together the flour and cornstarch. In another bowl, beat the egg.
Dip the chicken pieces first into the egg, then into the flour mixture, coating evenly.
Heat vegetable oil in a large skillet or wok over medium-high heat. Fry the chicken pieces in batches until golden and crispy, about 3-4 minutes. Remove the chicken and drain on paper towels.

🥄 Make the Sweet and Sour Sauce:
In a saucepan, whisk together the rice vinegar, sugar, ketchup, soy sauce, and pineapple juice (from the can of pineapple). Bring it to a simmer.
In a small bowl, mix the cornstarch with water to make a slurry, then add it to the sauce. Stir constantly until the sauce thickens, about 3-5 minutes. Set aside.

🔥 Cook the Vegetables:
In the same pan used for the chicken, stir-fry the bell peppers, onion, and pineapple chunks for 2-3 minutes until the vegetables are tender but still crisp.

🥢 Combine Everything:
Add the fried chicken back into the pan with the vegetables and pour the sweet and sour sauce over everything. Stir to coat all the ingredients evenly.
Cook for another 2-3 minutes, letting everything combine and heat through.

🍽️ Serve:
Serve the sweet and sour chicken over steamed rice or noodles.