• In a small bowl, whisk together the soy sauce, water, rice wine vinegar, corn starch, and black pepper.
• Pour this mixture over the sliced sirloin in a large ziplock bag.
• Seal the bag and shake gently until all the meat is coated. Refrigerate for at least 15 minutes.
• Heat 1 tablespoon of olive oil in a large wok or skillet over medium-high heat.
• Sauté the sliced peppers, the white part of the green onions, ginger, and garlic for about 3 minutes.
• Once softened, remove them to a plate.
• Add the remaining tablespoon of olive oil to the wok.
• Add half of the marinated steak, reserving the marinade liquid.
• Stir fry the steak for 2 to 3 minutes until it browns, then transfer to the plate.
• Repeat with the remaining steak, then transfer it to the plate as well.

Finish the Sauce

• Pour the reserved marinade into the wok.
• Cook and stir until it thickens, approximately 1 minute.
• Return the previously cooked steak and vegetables to the wok.
• Stir them together and cook for a couple of minutes until everything is heated through.
• Top with the green onion tops and give it one more stir.
• Serve immediately over rice or quinoa, allowing the sauce to soak into the grains for extra flavor.