In a mixing bowl, toss the pork pieces with the ginger, garlic and ¼ teaspoon crushed red pepper flakes. Let set while preparing the rest of the ingredients.

Prepare the sauce by mixing ¼ cup of the reserved pineapple juice with 6 tablespoons chicken stock, the ketchup, sugar, vinegar, soy sauce and remaining ¼ teaspoon crushed red pepper flakes in a small mixing bowl.

In another small bowl mix the remaining 3 tablespoons of chicken stock with the corn starch until well blended.

Heat a wok or large skillet over high heat. Add the oil and swirl it to coat the sides and bottom of the pan. Add the pork mixture and stir fry for 5 minutes or until cooked through. Remove the pork from the pan to a plate and set aside. Add the onions, peppers and sliced water chestnuts and stir fry until crisp-tender, about 3 minutes. Add the sauce mixture to the vegetables and cook, stirring until the sugar dissolves and it comes to a boil. Add the cornstarch mixture, the pork (along with any juices that have accumulated on the plate), the pineapple chunks and the maraschino cherries. Cook until everything is heated through and the sauce has thickened, about 2 minutes.

Garnish with sliced green onions and serve with hot rice.