Start by slicing the flank steak thinly against the grain, toss in cornstarch and let it sit for 10 minutes.

In a mixing bowl, combine soy sauce, brown sugar, minced garlic, grated ginger, and water or broth.

Heat vegetable oil in a large skillet over medium-high heat until shimmering.

Add the beef slices in batches, searing for 2-3 minutes on each side until browned.

Remove the cooked beef and pour the sauce into the skillet, simmering for 2-3 minutes.

Return beef to skillet and toss in the sauce, cooking for an additional 1-2 minutes.

Stir in green onions and cook for 30 seconds before serving.

Serve hot over jasmine rice, garlic noodles, or sautéed vegetables.