In a mixing bowl, combine soy sauce, pineapple juice, brown sugar, olive oil, garlic, ginger, black pepper, and red pepper flakes.
Add chicken thighs to the marinade, ensuring they are well coated.
Cover and refrigerate for at least 1 hour, preferably overnight.
Preheat your grill or oven to medium-high heat.
Remove chicken from the marinade, allowing excess to drip off.
Place chicken on the grill or a baking sheet if using the oven.
Grill for 25-30 minutes, turning occasionally, until cooked through.
Ensure the internal temperature reaches 165°F (74°C).
Remove from heat and let it rest for 5 minutes.
Garnish with fresh cilantro before serving.