Place flank steak in a glass or non-reactive flat dish. Mix together balsamic vinegar and Worcestershire sauce and pour over steak. Sprinkle steak seasoning on top of steak. Cover with plastic wrap and refrigerate 6-8 hours or overnight.
Remove the dish with flank steak from the refrigerator and allow to sit about 30 minutes at room temperature before grilling.
Preheat grill or grill pan to high heat. Brush with canola oil to prevent the steak from sticking. Place steak onto the grill or grill pan and cook on one side for about 3 minutes, until browned. Turn and grill the other side for about 3 more minutes. Reduce the heat to medium-low or move the steak to a cooler area of the grill and cook another 5 minutes until the steak reaches medium rare, 130º F - 140º F. Transfer to a cutting board, cover with foil and allow to rest for about 10-15 minutes. Thinly slice and serve.