Heat olive oil in a large skillet over medium heat.
Season chicken breasts with salt, black pepper, and garlic powder.
Sear chicken for 3-4 minutes per side until golden brown.
In a small bowl, mix brown sugar, soy sauce, and red pepper flakes.
Pour the sauce over the chicken and add pineapple chunks.
Cover and simmer for 10-12 minutes until chicken is cooked through.
In a separate bowl, mix cornstarch with water and stir into the skillet.
Cook for another 2 minutes until the sauce thickens.
Garnish with green onions and sesame seeds before serving.