Preheat oven to 425˚F. Line a large rimmed baking sheet with foil; lightly spray with cooking spray and set aside.
Place potatoes in a bowl; add oil, salt & pepper and mix to combine.
Transfer potatoes to prepared baking sheet and roast for 15 minutes.
In the meantime, add balsamic vinegar to a saucepan and bring to a boil over medium heat. Stir in brown sugar and cook for 3 minutes, stirring constantly, until mixture is slightly thickened. Remove from heat and set aside.
Lightly spray chicken breasts with cooking spray and season with salt and pepper. Place chicken breasts on top of potatoes
Reserve a tablespoon of the balsamic vinegar for later. Brush HALF of the remaining balsamic vinegar over the chicken breasts.
Bake for 20 minutes.
In the meantime, combine tomatoes with balsamic vinegar, oil and salt.
Remove baking sheet from oven; brush chicken with remaining half of the glaze, add tomatoes around the chicken, and continue to cook for 5 to 8 more minutes, or until internal temperature of chicken registers at 165˚F.
Remove from oven and drizzle with remaining tablespoon of balsamic glaze. Garnish with basil and serve with mozzarella cheese.