Season chicken thighs with salt and pepper.
Heat olive oil in a skillet over medium heat and sear chicken on both sides until golden brown, about 3-4 minutes per side.
In a small bowl, mix pineapple juice (from the can), brown sugar, soy sauce, garlic powder, and red pepper flakes.
Pour mixture over the chicken. Add pineapple chunks. Cover and simmer on low for 15–20 minutes until chicken is cooked through.
Mix cornstarch with water and stir into the skillet. Cook for another 2–3 minutes until the sauce thickens.
Garnish with green onions and sesame seeds if desired. Serve hot over rice or vegetables.