01 - In a mixing bowl, whisk together the soy sauce, pineapple juice, brown sugar, ketchup, minced garlic, grated ginger, and rice vinegar until the sugar dissolves. Reserve 1/4 cup of the mixture and set aside for basting later.
02 - Place the chicken thighs in a large resealable plastic bag or shallow dish. Pour the remaining marinade over the chicken, seal or cover, and refrigerate for at least 20 minutes or up to 2 hours for deeper flavor.
03 - Heat a large skillet over medium-high heat. Remove the chicken from the marinade, letting excess drip off, and discard the used marinade. Place the chicken in the skillet and cook for 4 to 5 minutes per side until golden brown and nearly cooked through. Transfer to a plate and set aside.
04 - In the same skillet, add the sliced red and yellow bell peppers, red onion, and pineapple chunks. Stir-fry for 4 to 5 minutes until the vegetables are just tender-crisp and the pineapple begins to caramelize slightly.
05 - Return the chicken to the skillet and pour in the reserved marinade. Bring to a simmer, then stir in the cornstarch slurry. Continue cooking for 2 to 3 minutes, turning the chicken occasionally, until the sauce is glossy and thickened and the chicken is fully cooked through.
06 - Transfer to a serving platter, spoon the pan sauce over the top, and garnish with sliced green onions and toasted sesame seeds. Serve immediately with steamed jasmine rice or cauliflower rice.