In a medium bowl, whisk together reserved pineapple juice, brown sugar, vinegar, soy sauce, ketchup and 1 ½ tablespoons of cornstarch.
Cut the chicken into 1-inch pieces and toss with ½ tablespoon of cornstarch and salt.
Heat the vegetable oil in a large skillet over medium-high heat. Add chicken and cook without stirring for 3 minutes or until browned on one side. Stir and cook for 6 -7 minutes or until cooked through. Transfer to a bowl and set aside.
Add the onion, red pepper, green pepper, ginger, and garlic to the skillet. Cook for 3 to 4 minutes or until softened.
Whisk the sauce and add it to the skillet with the pineapple. Simmer for 2 minutes or until slightly thickened. Add the chicken back to the skillet and stir to combine.
Serve over rice and garnish with green onions and sesame seeds.
