In a bowl, whisk together balsamic vinegar, olive oil, garlic powder, salt, and pepper.
Marinate the flank steak in the balsamic mixture for at least 30 minutes.
Preheat the grill to medium-high heat and grill the steak for about 5-7 minutes on each side, or until desired doneness.
Remove the steak from the grill and let it rest for 5 minutes before slicing.
In a large bowl, combine mixed greens, cherry tomatoes, corn, red onion, and Gorgonzola cheese.
Slice the steak thinly and place it on top of the salad.
Drizzle with additional balsamic vinegar if desired and serve immediately.