01 - Preheat a grill pan or skillet over medium-high heat.
02 - Cut chicken breasts horizontally to create even cutlets. Drizzle with olive oil and season both sides with salt and black pepper.
03 - Place chicken cutlets on the hot grill pan. Cook for 4 to 5 minutes on each side until golden and fully cooked. Remove from heat and let rest 2 minutes, then slice if preferred.
04 - Spread butter lightly on the inside of each roll. Toast cut sides on the grill pan until golden brown.
05 - Spread basil pesto evenly over the bottom half of each roll.
06 - Arrange grilled chicken, mozzarella slices, tomato, and arugula or spinach on top of the pesto. Complete each with the top half of the roll.
07 - Serve sandwiches warm or at room temperature.