01 - Warm grill pan or skillet over medium-high heat until hot.
02 - Slice chicken breasts horizontally to create thin cutlets. Drizzle with olive oil and season both sides with salt and pepper.
03 - Grill chicken for 4 to 5 minutes per side until fully cooked and golden brown. Transfer cooked chicken to a plate to rest for 2 minutes. Slice as desired.
04 - If desired, spread butter on the interior cut side of each roll. Toast on the grill pan or skillet, cut side down, until golden and crisp.
05 - Spread a generous layer of basil pesto on the bottom half of each roll.
06 - Arrange grilled chicken slices, mozzarella cheese, tomato slices, and baby arugula or spinach over the pesto. Cap with the remaining roll halves.
07 - Serve sandwiches warm or at room temperature.