Make the sauce: In a small bowl, whisk together soy sauce, honey, rice vinegar, toasted sesame oil, 2 tablespoons water, and red pepper flakes. Set near the stove.
Coat the pork: In a medium bowl, toss the sliced pork with salt, pepper, cornstarch, and 1 tablespoon water until every piece looks lightly frosted. Let it stand for 10 minutes while you heat the pan—this brief rest helps the coating adhere and the pork stay tender.
Sear in batches: Heat 1 tablespoon of the neutral oil in a large (12-inch) skillet over medium-high until shimmering. Add half the pork in a single layer. Cook undisturbed for 1 minute to brown, then stir-fry 2 minutes more until just cooked through. Transfer to a plate. Add the remaining 1/2 tablespoon oil and repeat with the remaining pork.
Aromatics: Return the empty skillet to medium heat. If the pan looks dry, swirl in a teaspoon more oil. Add the scallion whites, garlic, and ginger; stir-fry just until fragrant, about 30 seconds, scraping up any browned bits.
Glaze: Pour in the prepared sauce and bring to a lively simmer. Cook 1 to 2 minutes, stirring, until slightly thickened and glossy. Return the pork and any juices to the pan and toss for 30 to 60 seconds to coat and heat through.
Finish and serve: Remove from heat, fold in the scallion greens, and taste—add a splash more vinegar for brightness or salt to preference. Serve immediately over hot rice.