1. Prepare the beef by slicing it thinly across the grain to enhance tenderness. Marinate the beef with soy sauce, cornstarch, and a pinch of baking soda for at least 15 minutes.
2. Wash the bok choy, separate the stems from the leaves, and cut the stems into bite-sized pieces. Leave the leaves whole or coarsely chop them. Mince garlic and ginger, and slice onions thinly.
3. Heat a large skillet or wok over high heat with 1-2 tablespoons of vegetable oil. Sear the marinated beef in small batches to prevent overcrowding. Cook for 2-3 minutes per side until browned. Remove from the skillet and set aside.
4. Add more oil to the skillet if needed. Sauté the minced garlic, ginger, and sliced onions for 1-2 minutes until fragrant and slightly softened.
5. Stir-fry the bok choy stems for about 3-4 minutes, stirring frequently. Add any additional vegetables, such as broccoli or bell peppers, if desired.
6. Toss in the bok choy leaves once the stems are tender. Stir-fry for 1-2 minutes until the leaves wilt and soften.
7. Prepare the sauce by whisking together hoisin sauce, soy sauce, oyster sauce, sesame oil, and sriracha in a small bowl. Pour the sauce into the skillet, stirring well to coat all ingredients. Let the sauce simmer for 1-2 minutes to thicken slightly.
8. Return the cooked beef to the skillet and stir it into the sauce and vegetable mixture. Cook for an additional 2-3 minutes to reheat the beef and allow it to absorb the flavors.
9. Serve the Bok Choy Stir-Fried Beef hot over steamed rice, fried rice, or noodles. Garnish with sesame seeds, green onions, or chili crisp for an extra burst of flavor.