Spread sirloin strips on a plate or shallow bowl in a single layer. Sprinkle baking soda over the strips and toss lightly to coat. Refrigerate for 20 minutes.

Rinse meat strips with tap water and blot with paper towels to dry.

Stir cornstarch and water together in a small mixing bowl, making sure there are no lumps. Add sugar, soy sauce, Shaoxing wine, Chinese 5-spice powder, and white pepper. Stir to combine.

Remove all but 2 tablespoons of the liquid mixture from the mixing bowl and reserve. Add meat strips to the 2 tablespoons of liquid and toss to coat.

Heat vegetable oil in a large skillet or wok over high heat, and add the meat slices, spreading them flat. Cook undisturbed for 1 minute, then stir and cook another minute.

Stir in onion slices, julienned carrots, and green beans. Cook, stirring constantly, 1 to 2 minutes.

Add garlic and ginger. Cook and stir for about 30 seconds, and add the reserved liquid mixture and 1 cup stock or broth. Stir frequently until the vegetables are tender-crisp and the sauce is bubbly, 1 to 2 minutes. Stir in sesame oil, to taste.