Chicken Pesto Sandwich

Preheat oven to 350°F (177°C). Line a rimmed baking sheet with aluminum foil and set it aside.
One at a time, cut 1 pound chicken breasts in half horizontally through the center, creating two thinner pieces of each breast.
Set a large skillet over medium-high heat. When the pan is hot, add 1 tablespoons olive oil. When oil begins to shimmer, add the chicken cutlets.
Cook for 3-5 minutes on each side, flipping as sides get brown to ensure they don't burn. Set cutlets aside on a plate once cooked for 5 minutes.
In small bowl, mix remaining 1 tablespoons olive oil with ½ teaspoon salt and ½ teaspoon ground pepper.
Use basting brush to spread olive oil mixture on inside of 4 servings ciabatta rolls. Place bread onto frying pan for 30 seconds or until grill marks can be seen.
Remove bread and place onto baking sheet, face up. Spread 2 tablespoons pesto lightly on each piece of bread.
Slice cooked chicken into ½-inch pieces. Layer sliced chicken, ¼ cup of the 1 cup spinach, sliced 1 medium tomato, and sliced 8 ounces fresh mozzarella cheese onto bread
Drizzle 1 tablespoon balsamic vinegar over sandwich toppings.
Bake in preheated oven for 7-10 minutes, until cheese begins to melt.