Begin by slicing your beef flank steak into thin strips against the grain. In a mixing bowl, combine the beef with baking soda, light soy sauce, peanut oil, and cornstarch. Let this marinate for about 15 minutes at room temperature.

In a separate bowl, whisk together oyster sauce, dark soy sauce, sugar, and sesame oil until fully integrated. This mixture will become your flavorful sauce.

Heat 1 tablespoon of peanut oil in a large skillet over medium-high heat. Add the marinated beef and sear for about 1 minute on each side until golden brown.

Transfer the cooked beef to a plate. In the same skillet, add onion, garlic, and ginger. Sauté for about 2 minutes until translucent and fragrant.

Add the chopped asparagus and stir-fry for approximately 1 minute until they soften slightly while retaining their color and crunch.

Pour the prepared sauce mixture into the skillet with the aromatics and asparagus. Cook for about 1-2 minutes until the sauce thickens.

Return the seared beef to the skillet, gently tossing everything together for about 1-2 minutes until heated through.