Cut tenderized flank steak into four equal pieces.
In a dish large enough to fit your steak, mix grated ginger, garlic, soy sauce, sugar, and mirin. Place meat in the sauce and marinate at least 30 minutes and up to overnight.
When ready to cook, pour 1/2 to 1 inch layer of oil in a skillet with deep sides (cast iron works great for this). Heat oil on stovetop while you prepare your steak.
In a shallow dish, beat eggs until smooth and add green onions. Put flour in a separate shallow dish.
Use a paper towel to wipe off excess marinade from the flank steak. Then dredge each piece in flour and dip in the egg batter. Place immediately in the skillet with oil.
Fry battered meat for 1-2 minutes on each side. Remove cooked meat to a wire rack and let cool. Note: If your tenderized meat was thicker than 1/2 inch you may need to cook a minute or two longer per side.
When meat has cooled enough to handle, slice into strips (like katsu) and serve over rice.