Prepare the Chicken: Place chicken breasts between two pieces of plastic wrap and pound to an even thickness. Season with salt and pepper on both sides.

Cook the Chicken: Heat peanut oil in a large skillet over medium heat. Cook chicken for 5–7 minutes per side until golden brown and fully cooked. Transfer the chicken to a plate and keep it covered to lock in the juices.

Make the Sauce: In a bowl, whisk together cornstarch and cold water. In a saucepan, combine soy sauce, sugar, cider vinegar, garlic, ginger, and black pepper. Bring to a gentle simmer, then whisk in the cornstarch slurry and cook until thickened.

Cook the Vegetables: In the same skillet used for the chicken, sauté pineapple, red bell pepper, broccoli, and minced garlic for 1–2 minutes until fragrant and slightly tender.

Combine Everything: Cut the chicken into bite-sized chunks, return it to the pan, and pour the prepared teriyaki sauce over the mixture, stirring well. Let it cook for another 1–2 minutes until everything is evenly coated.

Serve: Plate over steamed jasmine rice or noodles. Garnish with green onions and sesame seeds.