Start by tenderizing the boneless, skinless chicken thighs with a meat mallet. Place them in a sturdy Ziploc bag.

In a mixing bowl, whisk together soy sauce, brown sugar, pineapple juice, sesame oil, freshly chopped garlic, and minced ginger until the sugar is dissolved. Pour marinade over the chicken, seal the bag tightly, and refrigerate for at least 4 hours or ideally overnight.

After marinating, pour the remaining marinade into a small saucepan. Bring to a gentle simmer over medium heat for about 5–10 minutes until it thickens.

Preheat your grill to medium-high heat (about 400°F or 200°C). Remove chicken from the marinade and discard the raw marinade. Lightly oil the grill grates. Cook chicken for about 6–8 minutes on each side until internal temperature reaches 165°F (75°C).

Remove grilled chicken from heat, let it rest for a couple of minutes, and drizzle thickened marinade over it. Optionally sprinkle with chopped green onions and serve with sticky rice or stir-fried vegetables.