01 - Season chicken pieces with salt and pepper in a bowl. Toss with 2 tablespoons cornstarch until evenly coated on all sides.
02 - Heat 1 tablespoon vegetable oil in a large skillet or wok over medium-high heat. Add half the chicken and cook for 3 to 4 minutes per side until golden brown and cooked through. Remove and repeat with remaining oil and chicken. Set aside.
03 - In the same skillet, add minced garlic and grated ginger. Sauté for 30 seconds until fragrant, stirring constantly.
04 - Pour in pineapple juice, soy sauce, brown sugar, rice vinegar, and ketchup. Stir to combine and bring to a gentle simmer.
05 - Stir in diced red bell pepper and pineapple chunks. Simmer for 3 to 4 minutes until vegetables begin to soften.
06 - Return chicken to the pan. Whisk the cornstarch slurry again and stir into the sauce. Cook for 2 to 3 minutes, stirring constantly, until sauce thickens and coats the chicken evenly.
07 - Remove from heat. Sprinkle with sliced green onions and sesame seeds immediately before serving.