Prepare the sauce, mixing together the water, teriyaki sauce, soy sauce, hoisin sauce, garlic, ginger, brown sugar and chili paste. Pour one cup of the sauce over the sliced beef in a reusable container and marinate for at least four hours.
1 pound flank steak, 3/4 cup water, 3/4 cup teriyaki sauce, 1/2 cup low sodium soy sauce, 3 tablespoons hoisin sauce, 6 cloves garlic, 3 tablespoons ginger, 2 tablespoon brown sugar, 3 teaspoons chili paste
Add the cornstarch to the remaining sauce, approximately 1 1/2 cups, whisking to combine. Store in the refrigerator until you are ready to make the stir fry.
2 tablespoons corn starch
Heat the oil in a large 12 inch skillet. Remove the beef from the marinade, and discard the remaining marinade. Add the sliced beef to the skillet and cook until browned, about 3 to 4 minutes. Use a slotted spoon to remove the beef from the skillet.
2 tablespoons vegetable oil
Add the vegetables to the skillet over medium-high heat. Stir to combine. Cover and cook until they are tender, another 5 to 7 minutes, stirring once or twice.
1 medium red bell pepper, 1 medium yellow bell pepper, 2 medium carrots, 1 head of broccoli
When the vegetables are tender, pour off any excess liquid. Add the sauce you prepared earlier and allow to thicken, about 1 to 2 minutes. You will know it is finished when the sauce thickens and darkens in color. Return the beef to the skillet and stir to combine.
Serve over rice.