For the sauce, in a small bowl whisk together cornstarch and soy sauce. Add in pineapple juice, honey, brown sugar, rice vinegar, ketchup and red pepper flakes. Heat 1 1/2 tsp of the oil in small saucepan over medium heat. Add ginger and garlic and saute until lightly golden brown, about 30 seconds - 1 minute. Whisk pineapple juice mixture once more then pour into saucepan. Bring mixture to a boil stirring constantly. Allow to boil, stirring constantly until thickened, 1 minute. Remove from heat