Season the steak: Season the flank steak with the crushed garlic, cumin, salt and pepper and set aside 5-10 minutes.
Make the salsa: Meanwhile, combine red onions, olive oil, lime juice, salt and pepper in a medium bowl and set aside a few minutes.
Add tomatoes, black beans, corn, cilantro and set aside.
Preheat the grill. Heat a clean lightly greased indoor or outdoor grill on high heat.
Grill the steak on high heat, 6-8 minutes on each side or until your desired degree of doneness. Until a probe thermometer inserted into the thickest part of the steak registers 130F to 135°F for medium to medium rare
Let the meat rest about 5 minutes before slicing.
Slice the beef into thin slices across the grain, place on a platter and top with corn, black bean and tomato salad.