Thinly slice the tomato and fresh mozzarella into 1/4 inch thick slices. Set aside.

Flatten each chicken breast using a rolling pin to 1/4 inch thick slices. Season with salt and pepper. Set aside.

Heat cast iron skillet or grill pan to medium heat, add a splash of olive oil and fully cook the chicken through, about 2-3 minutes per side. Set aside. Take a paper towel and carefully wipe up excess juices (if any).

Reduce heat to medium-low. Drizzle 1-2 teaspoons of olive oil on one side of each slice of panini bread (oiled sides facing the skillet when searing). Use a basting brush or the back of a spoon to spread the oil evenly. Assemble each panini right on the skillet starting with one slice of bread, chicken breast, mozzarella slices, pesto, tomato slices, and balsamic glaze. Top with the other slice of panini bread.

Sear for 2-3 minutes per side, periodically pressing down firmly with a large spatula on both sides so the panini sticks together and the cheese starts to melt. The panini is done when the bread is golden brown and crunchy. I may flip 2-3 times to ensure even cooking.