In a small bowl, whisk together the oyster sauce, low-sodium soy sauce, dark soy sauce, granulated sugar, pepper, and optional Sriracha until smooth. Set the sauce aside.

Thinly slice your beef into strips and place them in a mixing bowl. Sprinkle over the baking soda and garlic powder, then add 1½ tablespoons of the prepared sauce. Toss to combine and let marinate at room temperature for 15-20 minutes.

Heat a wok over high heat, adding a splash of cooking oil. Add the marinated beef in a single layer. Sear for 1-2 minutes until slightly pink, then transfer to a plate.

Add more cooking oil if necessary, then toss in the sliced onion and Chinese broccoli. Sauté for 1-2 minutes until the onions are slightly charred and the broccoli is vibrant green.

Toss in the rice noodles along with half of the reserved sauce. Gently stir until the noodles soften, about 1-2 minutes.

Add the bean sprouts and remaining sauce to the wok, mixing well. Cook for another 1-2 minutes until heated through.

Add the cooked beef back into the wok, tossing until warmed through. Serve immediately.