Step 1

In a medium bowl, combine the pork, 1 tablespoon of the sugar, 1 tablespoon of the soy sauce, ½ teaspoon of the MSG (if using), ¼ teaspoon salt and ¾ teaspoon pepper. Mix until the pork is thoroughly coated; set aside at room temperature for 30 minutes (for longer storage, cover and refrigerate for up to 2 hours).

Step 2

Meanwhile, in a small bowl, whisk together the remaining 3 tablespoons sugar, remaining 2 tablespoons soy sauce, remaining ¼ teaspoon MSG (if using), vinegar, apple jelly, ketchup, ¼ teaspoon salt and ½ teaspoon pepper; set aside until ready to use.

Step 3

When you are ready to cook, sprinkle the cornstarch over the pork and mix until evenly coated. In a 12- to 14-inch wok over high, heat the oil until barely smoking. Add half of the pork, separating the pieces and distributing them in an even layer. Cook, undisturbed, for 1 minute. Stir, then cook, stirring occasionally, until crisp and deeply browned on all sides, 5 to 7 minutes. Using a slotted spoon, transfer to a large plate and set aside. Using the oil remaining in the wok, cook the remaining pork in the same way and transfer to the plate. Pour off and discard all but 1 tablespoon of the oil.

Step 4

Return the wok to high and heat the oil until barely smoking. Add the pineapple, onion and bell pepper; cook, stirring once or twice, until spottily charred but still crisp, about 2 minutes. Transfer to another plate and set aside.

Step 5

Pour the sauce mixture into the wok and bring to a boil over medium-high. Cook, whisking to combine and to scrape up any browned bits, until the sauce is thick and syrupy and forms large bubbles across the entire surface, 5 to 7 minutes.

Step 6

Return the pork to the pan and cook, stirring and tossing, until well glazed, 2 to 3 minutes. Return the vegetable mixture and cook, tossing, until well coated, 1 to 2 minutes. Off heat, taste and season with salt and pepper.