Begin by marinating the flank steak. Combine the baking soda mixture, soy sauces, sesame oil, Shaoxing wine, black pepper, and sugar in a bowl. Toss in the thinly sliced flank steak, ensuring all pieces are coated. Let the meat marinate for about 30 minutes. This step is crucial for tenderness and flavor infusion.

While the meat soaks in all those flavors, chop your vegetables. Slice the bell peppers into thin strips and chop the onion. Mince the garlic and grate the ginger. Having everything ready makes the cooking process smoother.

After marinating, drain the steak and dust each piece lightly with cornstarch. This will create a crispy crust when cooked.

In a large pan or wok, heat peanut oil over high heat. Make sure it's hot enough that the oil shimmers but be cautious not to let it smoke.

Add the coated steak to the hot oil in small batches. Sear each side until browned and crispy, about 1-2 minutes per side. Remove the cooked steak and set it aside.

With the steak out of the pan, add more oil if necessary. Toss in the garlic and ginger first, followed by the chopped onion and bell peppers. Stir-fry these for about 3-4 minutes until they are tender yet crisp.

Return the cooked steak to the pan with the veggies. Pour in your sauce mixture and toss everything together for a couple of minutes until it's heated through. Let the sauce reduce slightly so it clings to the meat and veggies.

Once everything is beautifully combined, serve the Pepper Steak hot over a bed of steamed rice or noodles. Garnish with more black pepper if desired.