In a large mixing bowl, whisk together the soy sauce, ketchup, brown sugar, rice vinegar, toasted sesame oil, minced garlic, grated ginger, smoked paprika, and black pepper until the sugar is dissolved.

Add the boneless, skinless chicken thighs to the marinade, ensuring they are fully coated. Cover the bowl and refrigerate for at least 30 minutes, or ideally 2-4 hours for maximum flavor. You can also marinate overnight.

While the chicken marinates, cook the jasmine rice: Combine 1 1/2 cups jasmine rice with 3 cups water in a saucepan. Bring to a boil, then reduce heat to low, cover, and simmer for 15 minutes, or until water is absorbed and rice is tender. Remove from heat and let stand, covered, for 5 minutes before fluffing with a fork.

Core and slice the fresh pineapple into 4 rings, about 1/2 inch thick.

Preheat your grill or grill pan to medium-high heat. Lightly brush the grill grates or pan with olive oil to prevent sticking.

Remove the chicken thighs from the marinade, letting any excess drip off. Reserve about 1/4 cup of the marinade for basting (if using for basting, ensure it has not come into contact with raw chicken, or boil it vigorously for 5 minutes before use).

Place the chicken thighs on the preheated grill. Grill for 6-8 minutes per side, or until cooked through and an internal temperature of 165°F (74°C) is reached, basting occasionally with the reserved marinade during the last few minutes of cooking if desired.

While the chicken is cooking, add the pineapple rings to the grill. Grill for 2-3 minutes per side, until they have nice grill marks and are slightly caramelized.

Once cooked, remove the chicken and pineapple from the grill and let rest for a few minutes.

To assemble each stack, place a mound of fluffed jasmine rice on a serving plate. Top with one grilled Huli Huli chicken thigh, and then a grilled pineapple ring.

Garnish with chopped green onions and toasted coconut flakes (if using). Serve immediately.