Make the Marinade:

In a large bowl, whisk together the soy sauce, brown sugar, pineapple juice, rice vinegar, ketchup, minced garlic, grated ginger, and sesame oil. Taste and adjust seasoning with salt and pepper if needed.

Marinate the Chicken:

Place the chicken thighs (or breasts) into the bowl or a zip-top bag and pour the marinade over the chicken. Seal the bag or cover the bowl, then refrigerate for at least 1 hour, or up to 4 hours for deeper flavor. For the best results, marinate the chicken overnight.

Preheat the Grill:

Preheat your grill to medium-high heat. Brush the grill with a little vegetable oil to prevent sticking.

Grill the Chicken:

Remove the chicken from the marinade, reserving the marinade for basting. Grill the chicken for about 6-7 minutes per side, basting with the reserved marinade as it cooks. Ensure the chicken is cooked through and reaches an internal temperature of 165°F (75°C). If you're using a stovetop grill pan, cook the chicken over medium-high heat, flipping as needed to achieve an even grill mark.

Serve:

Once the chicken is cooked, remove it from the grill and let it rest for a few minutes. Slice the chicken, if desired, and garnish with sliced green onions and sesame seeds.