Prepare the Chicken
Pat chicken dry and season with salt and pepper. Toss with cornstarch and flour until evenly coated.
Fry the Chicken
Heat oil to 175°C / 350°F. Fry chicken in batches until golden and crispy. Drain and set aside.
Make the Sauce
In a saucepan, whisk ketchup, pineapple juice, sugar, vinegar, and soy sauce. Simmer gently.
Mix cornstarch with water and stir into sauce until thickened.
Cook the Vegetables
In a hot pan, sauté bell peppers and pineapple for 2–3 minutes until tender-crisp.
Combine
Add chicken to the pan, pour sauce over, and toss quickly to coat.
Serve Immediately
Garnish with sesame seeds or green onions if desired.