Preheat oven to 400 degrees F.
Dice chicken breasts into pieces then add to a 9x9 or larger baking dish.
To make the sauce, combine granulated sugar, brown sugar, white vinegar, 1/4 cup water, pineapple juice, honey, 2 tablespoons soy sauce, ketchup, garlic cloves, red pepper flakes, orange zest, and fresh squeezed orange juice.
In a small dish, make a paste of 3 tablespoons cornstarch to 3 tablespoons cold water. Stir until smooth. Add slurry to sauce mixture then stir sauce mixture well.
Pour sauce mixture over chicken.
Bake for 45 minutes. Remove from oven and let sit for 5 minutes or until sauce thickens.
To the chicken dish, stir in 2 tablespoons soy sauce and 1 tablespoon fresh orange juice. This is an important step, it cannot be skipped or the dish won't taste like orange chicken! It brings the orange flavors out and removes some of the sweetness.
Serve with cooked rice, green onions, and sesame seeds. Additional red pepper flakes can be added for heat.