In a small bowl, whisk together olive oil, garlic, mustard, salt and pepper. Pour into large plastic zipper bag. Place steak in the zipper bag. Refrigerate at least 4 hours, preferably overnight.

Allow steak to sit at room temperature (30 minutes) while the grill preheats to medium-high.

Grill steak until golden brown and slightly charred, 4 to 5 minutes. Turn the steaks over and continue to grill 3 to 5 minutes for medium-rare, 5 to 7 minutes for medium or 8 to 10 minutes for medium-well. After done grilling, place on cutting board covered with foil.

While the steak rests, mix together the tomatoes and mozzarella. Drizzle with a small amount of olive oil and season with salt and pepper to taste.

Cut steak against the grain in to thin slices and place on a serving plate. Top with tomato and mozzarella mixture. Then top with some basil leaves and a drizzle of balsamic glaze.