01 - Place a grill pan or skillet over medium-high heat and allow it to preheat thoroughly.
02 - Slice each chicken breast horizontally through the center to create two thinner cutlets. Drizzle both sides with olive oil, then season evenly with salt and ground black pepper.
03 - Arrange seasoned cutlets on the hot grill pan. Cook for 3 to 4 minutes per side until well-marked and fully cooked through, reaching an internal temperature of 165°F. Transfer to a plate and rest for 2 minutes.
04 - Lightly toast the cut ciabatta rolls on the grill pan or in a toaster until golden and crisp, if desired.
05 - Apply a generous layer of basil pesto to the bottom half of each toasted roll.
06 - Layer each sandwich bottom with a grilled chicken cutlet, followed by a slice of mozzarella cheese, fresh tomato slices, and a handful of arugula or spinach leaves.
07 - If using, spread mayonnaise on the top half of each roll.
08 - Place the top halves onto the sandwiches. Cut each sandwich diagonally in half and serve immediately while warm.