01 - In a mixing bowl, whisk together the soy sauce, pineapple juice, brown sugar, ketchup, minced garlic, grated ginger, and rice vinegar until well combined. Reserve 1/4 cup of the marinade and set aside for basting later.
02 - Place the chicken thighs in a large resealable plastic bag or shallow bowl. Pour the remaining marinade over the chicken, ensuring each piece is evenly coated. Seal 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, discarding the used marinade. Sear the chicken 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 fresh pineapple chunks. Stir-fry for 4 to 5 minutes until the vegetables are slightly softened but still retain their vibrant color.
05 - Return the seared chicken to the skillet. Pour in the reserved marinade and bring to a gentle simmer. Stir in the cornstarch slurry and continue cooking for 2 to 3 minutes, stirring frequently, until the sauce thickens and coats the chicken and vegetables evenly.
06 - Serve immediately while hot, garnished with sliced green onions and toasted sesame seeds if desired. Pair with steamed jasmine rice or cauliflower rice.