Prepare the chicken. Place a chicken-breast on a sheet of parchment-paper. Fold the paper on the chicken.
With a rolling-pin, pound the chicken-breast to thickness of a bit less than 1". Put aside and repeat with the remaining chicken-breast.
Blend the italian-seasoning, sea-salt, garlic-powder, onion-powder, and pepper in a small-bowl then stir to blend.
Brush the chicken with olive-oil, then sprinkle with the seasoning mix. Twist the chicken-breast, then oil and season the other hand.
Heat a grill or grill-pan over high-heat. Put the chicken-breasts on the grill and cook for 5-6minutes each side, or till the internal-temperature reads 155°F working with an instant read-thermometer (the chicken will come to appropriate temperatures at the next measure).
Top each chicken-breast with 2 slices fresh-mozzarella. Keep on grilling 3minutes, or till the cheese melted and the internal-temperature reads 165°F.
Put the chicken-breasts on a platter or individual-plates. Top each chicken-breast with 2-3pieces of fresh-tomatoes, then sprinkle with fresh-basil and extra salt and pepper to taste.
Before serving, drizzle with aged balsamic-vinegar or balsamic-reduction. Serve immediately.