1 1/2 pounds boneless pork shoulder, trimmed, cut into 2-inch-wide strips, and thinly sliced
3 tablespoons soy sauce, divided, plus more if needed
½ teaspoon plus 1 tablespoon white sugar, divided
1 tablespoon cornstarch
3 tablespoons grapeseed or other neutral oil
1 medium red bell pepper, stemmed, seeded and chopped
1 cup chopped fresh pineapple (½-inch chunks)
2 or 3 serrano chilies, stemmed, seeded and thinly sliced on the diagonal
1-inch piece fresh ginger, peeled and cut into matchsticks (about 3 tablespoons)
? cup unseasoned rice vinegar, plus more if needed
3 scallions, thinly sliced on the diagonal
In a medium bowl, combine the pork, 1 tablespoon soy sauce, the 1/2 teaspoon sugar and the cornstarch; stir until the pork is evenly coated.
In a 12-inch nonstick skillet over medium-high, heat the oil until barely smoking. Add the pork in an even layer and cook, stirring only once or twice, until the pork is lightly browned, 4 to 5 minutes.
Add the bell pepper and cook, stirring occasionally, until the pepper is lightly browned, 4 to 5 minutes.
Add the pineapple, chilies and ginger, then cook, stirring occasionally, until the pineapple begins to brown, 2 to 3 minutes.
Stir in the vinegar, the remaining 2 tablespoons soy sauce and the remaining 1 tablespoon sugar. Cook, stirring often, until the meat and vegetables are lightly coated with the sauce, 1 to 2 minutes.
Off heat, taste and season with additional soy sauce and vinegar. Transfer to a serving dish and sprinkle with the scallions.