Combine brown sugar, ketchup, vinegar, reserved pineapple juice, soy sauce, salt, and 2 teaspoons of the cornstarch, in a medium nonmetallic bowl. Whisk until dissoved and set aside.

Combine flour and remaining cornstarch in a resealable plastic bag. Add the chicken. Seal the bag and shake to coat. Transfer to a cutting board and lightly spray both sides with cooking spray.

Heat 1 teaspoon of the canola oil over medium-high heat in a large skillet. Swirl it to coat the bottom. Cook chicken on one side for 4 minutes or until golden on the bottm. Turn chicken and pour in remaining oil, spreading as much as possible. Cook for another 4 minutes or until golden and chicken is no longer pink the center. Transfer to a plate, and cover to keep it warm.

Add carrots, onion, and red bell pepper to the same skillet, and cook on medium high heat, stirring occasionally, for 2 to 3 minutes or until tender-crisp. Make a well in the center of the vegetables. Pour the pineapple juice mixture into the well. Cook for 1 to 2 minutes stirring occasionally, or until thickened. Add the pineapple chunks. Stir the vegetables into the sauce. Add the chicken and cook for 2 to 3 minutes more, stirring occasionally, or until heated through.