Add the ingredients for the sauce in a small bowl and mix well. Set aside.
Sprinkle the strips of sirloin with the ginger powder and black pepper. Mix by hand to coat evenly. Set aside.
In a skillet or wok, heat the oil and garlic over medium high heat for about 5 minutes to allow the garlic to infuse with the oil.
Add the seasoned strips of sirloin to the hot oil and stir fry until you no longer see any pink on the beef. About 5 minutes. Remove the meat to a bowl and set aside.
Now add the peppers and water chestnuts to the hot oil and stir fry for about 4 minutes.
Next, add the onion and continue stir frying until the onions are translucent.
Add the sirloin back in and give it a couple of stirs. Before you add the sauce, give it a stir because the cornstarch will have settled to the bottom. Stir the sauce into the meat and veggies. Raise the heat and continue stirring until sauce thickens.
Turn off the heat and toss in the green onion pieces. Give it a couple of stirs.
Serve hot over rice with plenty of sauce.
