Chef's Tip: It might be simpler to slice the meat into neat strips if it has been frozen for 30 minutes beforehand.
Cut the steak into ¼-inch-thick strips against the grain, then add the baking soda to a bowl and work the soda into the flesh for a minute.
Stir in the soy sauce, sugar, and cornstarch, cover, and put away to combine the other marinade ingredients. You may marinate it on the countertop for half an hour or cook it right away.
After removing the seeds and cores, finely slice the bell peppers and onion (chopped from pole to pole) into ¼-inch pieces.
Peel and finely chop the ginger and garlic as well.
In a small bowl, combine all the sauce ingredients (except from the cornstarch slurry components), whisk to combine, and put aside.
Mix the cornstarch and 1 tablespoon water in a small, separate bowl until there are no lumps.
Swirl one tablespoon of oil into a wok or big, high-sided pan over high heat until it begins to smoke moderately.
Add half of the meat to the pan and cook for approximately a minute, without moving, until well-seared. Then, sauté for a further minute or so, or until the food is barely cooked through with a few pink spots. Move it into a basin.
After using paper towels to clean the wok, repeat the process with the leftover meat and another tablespoon of oil.
After the entire beef is cooked and put aside, add the remaining tablespoon of oil and stir-fry the onion and peppers for one to two minutes, or until they are crisp-tender and faintly browned in places.
Stir in the minced ginger and garlic, then add the beef back to the wok and stir-fry it for 30 seconds.
Stir-fry the beef for 30 seconds or until the sauce thickens and the meat is cooked through, adding the bowl of sauce ingredients and a little amount of cornstarch slurry if needed.
Increase the amount of cornstarch slurry in the sauce if it's not thick enough. Add more water (or beef broth) if it's too thick.
Take off the heat and serve with sesame seeds on top.