Preheat oven to 400°. Line a large sheet pan with non stick foil or regular foil then parchment paper.
Season chicken lightly with a bit of garlic salt and fresh ground black pepper. Place seasoned chicken in a ziploc bag with 1/3 cup or cornstarch and shake to coat all pieces well. Set aside.
Arrange peppers and onions on sheet pan and then put chicken pieces evenly throughout the peppers and onions. Spray everything generously with olive oil spray.
Bake for about 20 minutes, until chicken is completely cooked through and veggies are tender. While they are cooking, make the sauce.
For the sauce, in a medium saucepan combine 1 cup water with the brown sugar, red pepper flakes, ginger, garlic, soy sauce, and rice vinegar. Bring to a boil over medium high heat.
Whisk together 4 Tablespoons water with remaining 2 Tablespoons corn starch to make a slurry. Add this to the sauce and stir until thickened. Remove from heat and cover until ready to use.
When the chicken and veggies are done, remove from oven. Add the pineapple pieces to the pan and pour the sauce over all. Toss well to coat with the sauce.
Serve over rice and garnish with green onions and/or cilantro if desired. Enjoy!