In a medium bowl, combine the sliced beef with soy sauce, cornstarch, sesame oil, and optional baking soda, then mix well and set aside for at least 15 minutes, or up to 30 minutes at room temperature.

Whisk together beef broth, soy sauce, oyster sauce (if using), rice vinegar, brown sugar, grated ginger, minced garlic, and cornstarch in a small bowl until smooth and set aside.

Heat 1 tablespoon of oil in a large skillet or wok over high heat until shimmering, then add the marinated beef in a single layer and cook for 1-2 minutes per side until browned, being careful not to overcrowd the pan.

Remove the cooked beef from the pan and set it aside, ensuring it is slightly undercooked as it will finish cooking with the vegetables.

Add the remaining 1 tablespoon of oil to the same skillet or wok, then add the broccoli and carrots and stir-fry for 2-3 minutes until slightly tender-crisp.

Add the bell pepper and onion, and continue to stir-fry for another 2-3 minutes until the vegetables are tender-crisp.

Stir in the snow peas or snap peas during the last minute of cooking.

Return the beef to the skillet with the vegetables, give the stir-fry sauce a quick whisk, and pour it over the beef and vegetables.

Cook, stirring constantly, for 1-2 minutes until the sauce thickens and coats everything, then remove from heat and serve immediately over rice or noodles.

Garnish with chopped green onions and sesame seeds before serving.