01 - Preheat a grill pan or skillet over medium-high heat.
02 - Slice each chicken breast horizontally to yield thinner cutlets. Drizzle with olive oil and season both sides with salt and black pepper.
03 - Cook chicken cutlets for 4 to 5 minutes per side until cooked through with golden grill marks. Remove from pan, let rest for 2 minutes, then slice if desired.
04 - If desired, lightly butter the cut sides of each roll. Toast buttered sides on the grill pan or skillet until crisp and golden.
05 - Spread a generous layer of basil pesto onto the bottom half of each toasted roll.
06 - Layer sliced grilled chicken, fresh mozzarella, tomato slices, and baby arugula or spinach. Cap with the top half of the roll.
07 - Serve sandwiches warm or at room temperature.