Start by pounding your chicken breasts thin between two pieces of plastic wrap. Trim off any fat.
Heat a nonstick skillet over medium-high.
Salt and pepper chicken breasts on both sides and place in hot skillet. Cook for about 4 minutes per side depending on how thick they are. You want to get some good browning on each side.
When chicken is cooked through drizzle with the balsamic syrup, top with the mozzarella and tomato. Turn off heat, put lid on and let the cheese melt for a minute of two.