Mash Knorr® Homestyle Stock - Beef, 1 teaspoon sesame oil, brown sugar, ginger and red pepper flakes in small bowl with fork until blended. Toss steak with ½ of the stock mixture.
Heat vegetable oil in large nonstick skillet over medium-high heat and brown steak, in 2 batches, stirring quickly, about 5 minutes. Remove steak and set aside.
Stir remaining stock mixture, water and broccoli into same skillet and cook covered until broccoli is crisp-tender, about 3 minutes. Blend cornstarch with reserved 1 tablespoon water and stir into skillet. Bring to a boil over high heat, then reduce heat to low. Return steak to skillet and heat through. Stir in remaining 1 teaspoon sesame oil. Serve, if desired, with hot cooked rice.