Marinate the pork: In a bowl, combine the sliced pork with soy sauce, oyster sauce, hoisin sauce, and cornstarch. Mix well and let it marinate for 10 minutes.

Prepare the vegetables: While the pork marinates, slice the bell pepper, julienne the carrot, and separate the broccoli into florets. Mince the garlic and grate the ginger.

Heat the oil: Heat vegetable oil in a large wok or skillet over high heat until shimmering.

Cook the pork: Add the marinated pork to the wok and stir-fry for 3-4 minutes until browned. Remove the pork and set aside.

Stir-fry the vegetables: In the same wok, add garlic and ginger, stir-fry for 30 seconds until fragrant. Add bell pepper, carrot, and broccoli. Stir-fry for 3-4 minutes until vegetables are crisp-tender.

Combine and finish: Return the pork to the wok. Add green onions, sesame oil, and red pepper flakes if using. Toss everything together and cook for another minute. Serve hot over rice.