Toss the flank steak with cornstarch in a plastic bag until all the pieces are coated. Empty the beef into a colander then shake off excess cornstarch. Set aside.
Heat 1 Tablespoon oil in a large skillet or wok over medium-high heat. Add asparagus then saute for 1 minute. Add garlic and ginger then saute until extremely fragrant, 30 seconds, being careful not to let the garlic burn. Add Tamari, water and brown sugar then turn heat down to medium and let the sauce simmer for 2 minutes. Pour the mixture into a bowl then set aside.
Heat remaining 1-1/2 Tablespoons oil in the same skillet over high heat. Add the beef and cook, stirring every so often, until it is just barely cooked. Some pink still showing is ok. Add the sauce with asparagus back into the skillet, turn the heat down to medium-low, then simmer until sauce reaches your desired thickness.