To make the sauce, in a bowl, combine 1/4 cup of stock, the ketchup, sugar, juice, vinegar, soy, and 1/2 teaspoon of the pepper flakes. Set aside.
In a small bowl, combine the cornstarch with the remaining 2 tablespoons of stock and stir to dissolve. Set aside.
In a bowl, toss the shrimp with the ginger, garlic, and remaining 1/4 teaspoon pepper flakes. Set aside for 10 to 20 minutes.
Heat a large wok over high heat. Add the oil, swirling to coat the sides and bottom of the pan. Add the shrimp, garlic, and ginger and stir-fry until pink, about 2 minutes. Remove from the pan. Add the onions and peppers and stir-fry until crisp-tender, about 2 minutes. Add the sauce and cook, stirring, until the sugar dissolves. Add the cornstarch mixture and bring to a boil. Return the shrimp to the pan and add the pineapples, cherries, and green onions. Cook until the sauce is thick, about 1 minute.