
Combine the pork with all the marinade ingredients in a medium-sized bowl. Mix well. Marinate for 15 minutes while preparing the rest of the ingredients.
Mix all the sauce ingredients together in a small bowl.
Heat 1 tablespoon of oil in a wok or large non-stick skillet over high heat until smoking. Spread the pork with minimal overlap, cooking in two batches if needed. Let cook for 1 minute without moving, until the bottom turns golden. Flip to cook the other side for 30 seconds, until just cooked through. Transfer the pork to a large plate.
Add the remaining 1 tablespoon oil and garlic. Stir fry until fragrant, 20 seconds or so. Add the onion and the bell pepper. Cook and stir until starting to turn tender, 1 to 2 minutes.
Mix the sauce again to fully dissolve the cornstarch. Pour into the pan and add back the pork. Immediately stir to mix well. The sauce will thicken very quickly, in a couple of seconds. Turn off the heat and drizzle in the sesame oil. Toss again to mix. Transfer everything to a large plate. Serve hot as a main dish.