In a medium bowl, combine brown sugar, soy sauce, olive oil, minced garlic, grated ginger, black pepper, and red pepper flakes (if using). Whisk until the mixture is well blended.
Place chicken breasts in a large resealable bag or a shallow dish. Pour the marinade over the chicken, ensuring all pieces are well coated. Seal the bag or cover the dish and marinate in the refrigerator for at least 30 minutes (up to 4 hours for more flavor).
Preheat your grill or a skillet over medium-high heat. If grilling, lightly oil the grill grates or if using a skillet, add a dash of olive oil.
Remove the chicken from the marinade, allowing excess to drip off. Save the leftover marinade for the sauce. Cook the chicken for 6-7 minutes on each side, or until it reaches an internal temperature of 165°F (75°C).
In a small saucepan, heat the leftover marinade over medium heat and bring it to a boil. Let it simmer for 3-5 minutes until it thickens slightly to create a glaze.
During the last few minutes of chicken cooking, add the pineapple chunks to the grill or skillet, and cook until caramelized, about 2-3 minutes.
Once the chicken and pineapple are cooked, remove them from the heat. Drizzle the thickened glaze over the chicken and top with caramelized pineapple.
Garnish with chopped green onions and sesame seeds before serving.
Notes
Marinate the chicken for up to 4 hours for enhanced flavor.