1. Place the beef in a glass baking dish.

2. In a small bowl, whisk together the balsamic vinegar, olive oil, and garlic powder to make a marinade. Pour the marinade over the beef. Cover the dish and allow to marinate for 8 hours in the refrigerator.

3. Heat a cast iron grill pan over medium heat until hot. Add beef, discarding the marinade, and cook 6 minutes on each side or until the internal temperature reaches 145°F for medium rare.

Remove the steak from the skillet and place on a clean cutting board. Let rest for 10 minutes before slicing. Cut the beef into 1/4-inch thick slices, slicing against the grain.

4. To assemble the skewers: Add one basil leaf to a skewer followed by a cube of mozzarella, a slice of cooked beef, a grape tomato, and another basil leaf. Place on a serving platter. Keep refrigerated until ready to serve.