In a medium saucepan, heat the sesame oil over medium heat. Add the ginger and garlic, and sauté until the garlic begins to brown, about a minute. Add the low sodium soy sauce, ½ cup water and brown sugar.
Stir to combine until the brown sugar is completely dissolved. Bring the mixture to a boil for about 10 minutes, stirring occasionally, so that it thickens, then remove from the heat and set aside.
Slice the flank steak across the grain into strips and toss with the cornstarch, shaking off the excess.
In a large saucepan heat ¼ cup of vegetable oil over medium-high heat and sear the beef in batches making sure it is browned on all sides, but barely cooked in the middle.
When the beef is browned, remove from the pan to a plate lined with paper towels. Drain the excess oil from the pan.
Place the sauce in the pan used to cook the meat and bring it back to a boil. Add the cooked beef and continue to cook for 2 minutes. The sauce will continue to thicken.
Remove from the heat. If you want to add a little heat to this dish, add a teaspoon of chili flakes.
Serve over white rice, topped with green onions and sesame seeds. Pairs well with roasted broccoli.