Make the sauce: In a bowl, whisk pineapple juice, soy sauce, honey, rice vinegar, sesame oil, and red pepper flakes.
Taste and adjust sweetness or saltiness. Set aside. Stir together cornstarch and water in a separate small bowl.
Prep the chicken: Pat chicken dry and season lightly with salt and pepper.
Dry chicken browns better and stays juicier.
Sear in batches: Heat oil in a large skillet over medium-high. Add half the chicken in a single layer. Sear 2–3 minutes per side until browned and mostly cooked.
Transfer to a plate and repeat with remaining chicken.
Sauté aromatics: Reduce heat to medium. Add a splash of oil if needed. Cook white parts of green onion, garlic, and ginger for 30–45 seconds until fragrant.
Add peppers and pineapple: Stir in bell pepper and pineapple.
Cook 2–3 minutes to soften slightly and caramelize edges.
Simmer with sauce: Return chicken to the pan. Pour in the sauce and bring to a gentle simmer for 1–2 minutes.
Thicken: Stir the cornstarch slurry, then slowly pour it into the pan while stirring. Simmer another 1–2 minutes until the sauce turns glossy and clings to the chicken.
Finish: Turn off heat.
Stir in green onion tops. Taste and adjust with a squeeze of lime, extra honey, or a splash of soy if needed.
Serve: Spoon over rice or cauliflower rice. Garnish with sesame seeds and extra green onions.