In a bowl, combine oyster sauce, 2 teaspoons cornstarch, 1/4 teaspoon black pepper, and baking powder. Mix well.

Add the thinly sliced flank steak to the mixture and marinate for at least 10 minutes.

In a separate small bowl, combine beef broth, Chinese rice wine, dark soy sauce, sugar, and the remaining 1/4 teaspoon black pepper to create the sauce.

Heat a wok over high heat until very hot. Add 1 1/2 tablespoons of cooking oil, swirling to coat the sides.

Add minced garlic and ginger to the wok and cook until fragrant.

Add the marinated beef and stir-fry until no longer pink, approximately 1 1/2 to 2 minutes. Remove the beef from the wok and set aside.

Add the remaining 1/2 tablespoon of cooking oil to the wok, swirling to coat the sides.

Add the julienned bell peppers and stir-fry for 1 minute. Then, add 2 tablespoons of water.

Continue stir-frying for another 2-3 minutes, until the bell peppers are tender-crisp.

Return the cooked beef to the wok and add the prepared sauce.

Bring the mixture to a boil. Then, add the cornstarch solution (1 teaspoon cornstarch dissolved in 2 teaspoons water), stirring constantly until the sauce boils again and thickens.

Garnish with sliced fresh jalapeno and serve hot with rice.