01 - Preheat grill pan or skillet over medium-high heat.
02 - Slice chicken breasts horizontally to obtain thin cutlets. Drizzle with olive oil, then season evenly with salt and black pepper.
03 - Grill chicken cutlets for 4 to 5 minutes per side until fully cooked and golden. Transfer to a plate and let rest for 2 minutes. Slice if desired.
04 - Optional: Spread butter lightly on the inside of each bun. Place cut sides down on the grill pan or skillet and toast until golden.
05 - Spread a generous layer of basil pesto onto the bottom half of each roll.
06 - Arrange grilled chicken, mozzarella slices, tomato slices, and arugula or spinach over the pesto. Cover with the top half of the roll.
07 - Serve the sandwiches warm or at room temperature.