<ol><li><strong>Marinate the Beef:</strong> In a bowl, combine sliced beef with 1 tbsp soy sauce, 1 tbsp rice vinegar, and 1 tbsp cornstarch. Let it marinate for 10-15 minutes.</li><li><strong>Prepare the Sauce:</strong> In a small bowl, whisk together the remaining soy sauce, oyster sauce, hoisin sauce, rice vinegar, and sesame oil. Set aside.</li><li><strong>Stir-Fry the Beef:</strong> Heat vegetable oil in a large pan or wok over high heat. Add the beef in batches and stir-fry for about 2-3 minutes until browned and cooked through. Remove from the pan and set aside.</li><li><strong>Stir-Fry the Vegetables:</strong> In the same pan, add a bit more oil if needed. Stir-fry the garlic, ginger, onion, bell pepper, zucchini, carrot, and chili for about 3-4 minutes until tender-crisp.</li><li><strong>Combine and Toss:</strong> Add the beef back into the pan, pour the sauce over, and toss everything together. Stir-fry for another 1-2 minutes until everything is evenly coated and heated through.</li><li><strong>Serve:</strong> Remove from heat, garnish with fresh cilantro, and serve hot over cooked rice.</li></ol>