01 - Heat a grill pan or skillet over medium-high heat until hot.
02 - Slice the chicken breasts horizontally to create thin cutlets. Drizzle with olive oil and season both sides with salt and black pepper.
03 - Grill the chicken cutlets for 4 to 5 minutes per side until cooked through and golden. Remove from heat and rest for 2 minutes before slicing if preferred.
04 - Lightly butter the cut sides of each roll. Toast, buttered side down, on the grill or skillet until golden brown.
05 - Spread a generous amount of pesto on the bottom half of each roll. Layer grilled chicken, mozzarella slices, tomato slices, and arugula or spinach on top. Cover with the upper half of the roll.
06 - Serve sandwiches warm or at room temperature.