Mongolian Beef (PF Chang's copycat)

Make the sauce. Heat 1 tablespoon Vegetable oil in a medium saucepan over medium heat. Add ginger and garlic and stir for 30 seconds. Add soy sauce, water, and brown sugar. Bring to a boil and simmer until thickened some, 10 to 15 minutes. Slice flank steak against the grain into 1/4-inch slices with the knife held at a 45 degree angle. Some of the really long pieces I cut in half to make them more bite-sized. Toss flank steak with cornstarch and let sit 10 to 15 minutes. Heat 1 cup Vegetable oil in a large pan over medium-high heat. Add beef (I cooked it in 2 batches) and cook 2-3 minutes, until brown and crispy, flipping pieces over to cook both sides. Remove meat with a slotted spoon and discard cooking oil. Place meat back in pan along with sauce and cook over medium heat for 1 minute, stirring to coat meat. Add red pepper flakes and green onions and remove from heat. Serve over rice.