1. In a small bowl, whisk together soy sauce, oyster sauce, cornstarch, water, rice vinegar, honey, garlic, ginger, sesame oil, and red pepper flakes (if using). Set aside.

2. Heat 1 tablespoon of vegetable oil in a large skillet or wok over medium-high heat. Add the beef strips and stir-fry for 2-3 minutes, until browned and just cooked through. Remove and set aside.

3. In the same skillet, add the remaining oil. Stir-fry the bell peppers and onion for 4-5 minutes, or until they are tender but still crisp.

4. Return the beef to the skillet and pour in the prepared sauce. Stir well to coat everything evenly. Cook for an additional 2-3 minutes, allowing the sauce to thicken.

5. Remove from heat and serve hot over steamed rice or noodles. Garnish with sesame seeds or green onions if desired.