Prepare sauce: whisk together sauce ingredients, except for cornstarch and cold water; set aside. Stir together cornstarch and cold water and set aside.
Heat 1 tablespoon of the peanut oil in a large skillet or wok over medium high heat. When the oil starts to smoke, add the sliced beef and stir for 3 minutes. Remove beef to paper towels.
Add an additional 1 tablespoon of peanut oil to the skillet, then add vegetables, garlic and ginger. Stir constantly until vegetables begin to soften, about 4 minutes.
Return beef to skillet with vegetables and lower heat to medium-low. Clear a spot in the center of the skillet and add peanut mixture and cornstarch/water mixture. Stir for a few seconds, then toss with vegetables and beef. Cover and cook for 5 minutes.