See note in instructions.
Note: Mom’s original recipe for the slurry called for 1 tablespoon cornstarch, 1/2 cup water, and 1 tablespoon soy sauce.
In a medium-sized bowl, mix the marinade ingredients, the soy sauce, oyster sauce, sugar, and baking soda. (Baking soda is my addition; it helps to tenderize the beef.)
Add the cornstarch to a small cup, then add water, bit by bit as you mix. Add the 3 tablespoons soy sauce and 1 teaspoon dark soy. Set aside. The slurry may settle; stir back together before using.
Note: If you don’t use dark soy, you may add an additional tablespoon Soy sauce; go by taste so the dish doesn’t become too salty.
For easier slicing, freeze beef for 20 to 25 minutes until stiff, but not frozen. Slice with the grain into sections about 2 to 2 1/2 inches wide, then holding the knife at an angle, cut across the grain into very thin slices. Place in bowl with the marinade and toss together. Cover and refrigerate for 30 minutes to overnight.
Heat 2 tablespoons oil in a large skillet or a wok over medium-high heat until hot. Add onion and cook two to three minutes, stirring often. Add the green pepper and stir until slightly softened but still crisp, four to six minutes. Make well in the center; add garlic and ginger, and dow see if using, and stir constantly until fragrant (about a minute). Quickly toss the vegetable mixture together and remove from pan. The vegetables will continue to cook just a little as they sit and steam.
If needed, work in batches, half the oil and half the beef at a time. Add the remaining 2 tablespoons of oil and heat briefly. Add beef and cook, stirring as needed, until the meat picks up a little color; don’t overcook. It will finish cooking in the sauce.
As soon as the meat is ready, stir the cornstarch slurry if it has settled and stir it into the skillet. Allow to come to a boil. Quickly add the onion/bell pepper mixture back into the skillet, stir. Turn off heat, add the tomatoes, and allow to heat through.
Serve with rice.