Prepare the Chicken: Season the chicken breasts with salt, pepper, and a drizzle of olive oil. Heat a skillet or grill pan over medium-high heat.
Cook the Chicken: Grill the chicken for 6-7 minutes per side until fully cooked (internal temperature should reach 165°F/74°C). Once done, allow the chicken to rest for a couple of minutes before slicing it thinly.
Toast the Bread: Lightly toast the slices of bread in a toaster or on a griddle for extra crispness.
Assemble the Sandwich: Spread a generous layer of pesto sauce on one side of each slice of toasted bread.
Layer the Ingredients: Place one slice of mozzarella cheese (about 1 oz) on one piece of bread, followed by a portion of the sliced chicken. Optionally, drizzle with balsamic glaze for added flavor.
Grill (Optional): For a grilled version, heat a small amount of olive oil in a skillet and grill the assembled sandwich, pressing it down slightly, for about 2-3 minutes on each side until golden brown and crispy.
Serve: Once the sandwich is perfectly grilled, slice it in half and serve immediately, garnished with fresh basil if desired.