In a large bowl, whisk together soy sauce, pineapple juice, brown sugar, minced garlic, grated ginger, and optional chili flakes for heat. Add the chicken thighs, ensuring they are fully coated in the marinade. Cover the bowl and refrigerate for at least 4 hours, ideally overnight.

Prepare the sticky rice according to the package instructions. Rinse the rice under cold water until the water runs clear, then cook it in a rice cooker or saucepan. Once fluffy, remove from heat, fluff with a fork, and set aside.

Preheat your outdoor grill to medium-high heat (about 375°F to 400°F). Lightly oil the grill grates to prevent sticking. Slice a firm pineapple into rings.

Place the marinated chicken thighs directly on the grill. Cook for 6-7 minutes on each side, or until the internal temperature reaches 165°F.

Add the pineapple slices to the grill. Grill each slice for 2-3 minutes per side until caramelized.

On a serving platter, create a base layer with a generous scoop of fluffy sticky rice. Top with grilled chicken thighs and then with caramelized pineapple slices.

Drizzle any reserved marinade glaze over the stack and garnish with chopped green onions, toasted sesame seeds, and fresh cilantro.