The best way to handle slice the beef is partially frozen. Slice thinly, about 1/4-inch thick and 2-3-inches long.
Combine the rest of ingredients except for the oil, water, cornstarch. Marinate for about 30 minutes.
Heat oil in skillet and remove the garlic and onions from the marinade. Carefully sauté in hot oil for about 5 minutes. Drain the beef from marinade and add to the skillet. Stir-fry on medium-high heat, stirring often until cooked and browned. This should roughly take about 8 minutes, depending on your stove and thickness of meat.
Add the water and cornstarch to marinade and bring to a boil, stirring often. Mixture should start to thicken up but not too much. Slightly less than thick gravy consistency. Taste and adjust seasoning if needed. Lower temperature down and simmer for about 15 minutes more, careful not to burn. Serve over hot rice.