Marinade: In a bowl large enough to fit the beef, mix oil, soy sauce, and cornstarch into a paste. Slice the beef in 1/4" slices, against the grain. Toss well in the soy and cornstarch mixture, and let sit for 30 minutes at room temperature.
Frying: In a shallow skillet, heat the remaining oil on high heat so that it is really hot. While you are waiting for it to heat, coat the beef in the remaining cornstarch. Carefully lower one piece of beef into the oil to see if it is hot. If hot enough to fry the beef, place the rest of it in the pan and cook for about a minute or two, turning once. Once crispy, take the beef out of the pan and allow it to drain on a plate with paper towels. Discard all of the oil except for about a tablespoon.
Stir Fry: Add the garlic, ginger, chili, remaining soy sauce, and scallions, and stir fry well until garlic is nicely browned. Lower the heat. Add the vinegar and brown sugar and cook, stirring well until the vinegar is reduced and the sugar dissolved. Return the beef to the pan and cook for another 30 seconds until everything is coated nicely. Top with the fresh Scallions and serve with rice or noodles.
