Preheat your grill to medium-high heat.
Rub the flank steak with olive oil, garlic powder, onion powder, salt, and pepper.
Place the steak on the grill and cook for about 4-5 minutes per side for medium-rare, or until desired doneness. Remove from the grill and let it rest for 5-10 minutes.
While the steak is resting, prepare the salad. In a large bowl, combine the mixed greens, cherry tomatoes, avocado, blue cheese, and red onion.
Slice the rested steak against the grain into thin strips.
Top the salad with the sliced steak and drizzle with balsamic vinaigrette. Toss gently to combine.
Serve immediately and enjoy!