Preheat the oven to 400°F. In a small bowl mix together the chicken spice rub: 1 teaspoon dried thyme, ½ teaspoon garlic powder, ½ teaspoon salt, ¼ teaspoon ground black pepper.
Place 4 chicken breasts in a baking dish. Sprinkle the spice rub onto both sides then drizzle the chicken with olive oil.
Place the chicken in the oven to bake for 20 minutes.
While the chicken is baking, make the balsamic reduction. Add ½ cup balsamic vinegar and 2 tablespoon brown sugar to a saucepan over medium-high heat. Bring to a gentle simmer while stirring occasionally. Let this cook for about 10 minutes, or until the sauce begins to thicken and form a syrup-like consistency. Note: The sauce will thicken more as it cools down.
Once the chicken has cooked for 20 minutes, add slices of mozzarella cheese and a tomato slice to each one.
Place back in the oven to bake an additional 5-10 minutes, or until chicken is fully cooked reaching an internal temperature of 165F when poked with a meat thermometer.
Add the chicken to serving plates. Top with ½ cup sliced basil and drizzle the balsamic sauce on top with a spoon. Let the chicken rest for 5 minutes before slicing to allow the juices inside to redistribute. Now the chicken is ready to serve.