Start the rice according to package directions so it finishes while you prepare the chicken. Fluff with a fork and keep warm.
Pat the chicken pieces dry. Season with salt and pepper. Heat oil in a large skillet over medium-high heat. Add chicken in a single layer and cook 5–7 minutes, stirring occasionally, until golden on the edges and cooked through (165°F internal temperature). Transfer to a plate.
In the same skillet, lower heat to medium. Add pineapple juice, soy sauce, brown sugar, vinegar, garlic, and ginger. Stir and bring to a gentle simmer for 2 minutes so the sugar dissolves and the garlic becomes fragrant.
Stir the cornstarch slurry until smooth, then pour it into the simmering sauce. Cook 1–2 minutes, stirring constantly, until the sauce turns glossy and coats the back of a spoon.
Return the chicken to the skillet along with the pineapple chunks and red bell pepper. Toss everything in the sauce for 2–3 minutes until the chicken is well coated and the pepper softens slightly but still has bite. Taste and adjust seasoning if needed.
Divide warm rice among four bowls. Spoon the glazed chicken, pineapple, and peppers over the top. Sprinkle with green onions and sesame seeds. Serve immediately while the sauce is still glossy.