Preheat the air fryer to 375°F (190°C).
- Toss chicken cubes with cornstarch, salt, and pepper until well coated.
- Arrange chicken and bell pepper pieces in the air fryer basket in a single layer. Cook for 5 minutes, flip, then cook another 5–6 minutes until chicken reaches 165°F and is golden.
- Meanwhile, in a saucepan combine pineapple juice, soy or teriyaki sauce, BBQ sauce (if using), brown sugar, garlic, and ginger. Bring to a simmer until sugar dissolves.
- Add cornstarch slurry to the sauce, stirring until thickened and glossy, about 1–2 minutes.
- Stir in air-fried chicken, bell peppers, and pineapple chunks until coated evenly in the sauce.
- Serve hot over rice, quinoa, or cauliflower rice. Garnish with green onions or sesame seeds if desired.