Whisk all sauce ingredients together. Re-whisk just before using at the end.
Heat up a wok with 1 tablespoon of the cooking oil to 400. Check temperature with infrared temperature gun, or heat until oil is shimmering.
Add the beef to the wok and do not disturb for 30-40 seconds. Stir fry the beef for another 30-40 seconds.
Remove the beef from the wok and into a bowl. Set aside.
Clean the wok using tongs and a bunched up wad of paper towels. Heat it up with the remaining 2 tablespoons of oil.
Add in the minced ginger and sliced garlic and stir-fry until light brown or aromatic. About 30 seconds.
Add the bell peppers and scallion bottoms to the wok and do a few quick stirs.
Add the beef back in and do a few quick stirs.
Re-whisk sauce, and pour down the edges of the wok so it slides down the sides. Do not pour over top.
Continue to stir fry making sure everything is well blended with the sauce and all of the ingredients, about 30-60 seconds.
Remove from heat and pour toasted sesame oil over top and stir in.
Transfer over top of noodles in the two bowls using tongs. Spoon more sauce over if needed.
Garnish with the scallions.
Serve immediately.