Prep the Ingredients: Slice the beef, bell peppers, and onion. Mince the garlic. Cook the rice if not already prepared.
Cook the Beef: Heat oil in a large pan or wok over high heat. Add the beef strips, season with salt and pepper, and sear for 2–3 minutes until browned. Remove from pan and set aside.
Stir-Fry the Veggies: In the same pan, add a bit more oil if needed. Stir-fry bell peppers, onion, and garlic over medium-high heat until slightly tender but still crisp.
Combine Everything: Return the beef to the pan. Add soy sauce and rice vinegar. Stir everything together and cook for another 2–3 minutes until heated through and well coated.
Serve: Spoon the beef and vegetable mixture over hot cooked rice. Garnish with fresh herbs if desired, and serve warm.