This is another American-born Chinese dish that is part of our wok vocabulary. I will always firmly believe that dishes, like Mongolian beef and California roll, that were born in the States are authentic dishes. The secret to tender meat in the wok is the marinade. You will see this in many of my recipes. Baking soda tenderizes the meat, cornstarch and water create a slurry that brings in the baking soda and oil pre-lubricates the meat and keeps us from using too much oil in the wok.
For the beef: Slice the flank steak across the grain into 3/4-inch (19 millimeters)-thick slices on an angle to make planks then cut the planks into 3/4-inch (19 millimeters) cubes. Combine the cornstarch, baking soda and salt with 2 tablespoons of water in a small bowl and set aside. Place the steak in a shallow bowl and add the water, vegetable, and cornstarch mixture. Massage all the ingredients into the meat. Cover and refrigerate for 2 to 12 hours.
For the sauce: Combine the oyster sauce, hoisin sauce, soy sauce, cornstarch, vinegar, garlic and half the ginger in a small bowl and set aside.
For the stir-fry: Heat the oil to medium-high in a wok or medium saute pan. Stir in the beef and cook to medium-rare, stirring constantly, about 3 minutes. Drain off excess oil. Add the garlic and remaining ginger and saute 20 to 30 seconds. Stir in the bell peppers and onions and let them cook until the edges of the onion and bell peppers begin to brown, about 2 minutes. Add the scallion whites, dried chilies and sauce, stir constantly and let it cook for about 2 minutes, until the sauce thickens.
Transfer to a platter and garnish with the scallion greens.