In a small bowl, whisk together the olive oil, Worcestershire sauce, balsamic vinegar, minced garlic, thyme, black pepper, and minced onion.
Place your steak in a large resealable plastic or food storage bag, airtight container or shallow dish.
Pour the marinade over the steak, making sure it is completely covered.
Seal the bag or cover the dish with plastic wrap and refrigerate for at least 2-4 hours, or preferably overnight.
When you are ready to cook the steak, preheat your broiler on high heat.
Remove the steak from the marinade and pat it dry with paper towels to remove excess moisture.
Place the steak on a broiler pan and broil for about 5-7 minutes per side for medium-rare doneness or until meat thermometer reaches an internal temperature of 130-135 degrees Fahrenheit.
Let the steak rest for a few minutes before slicing against the grain and serving.