01 - Preheat grill pan or skillet over medium-high heat.
02 - Slice chicken breasts horizontally to form thinner cutlets. Drizzle each with olive oil and evenly season with salt and black pepper.
03 - Grill chicken cutlets for 4 to 5 minutes per side until thoroughly cooked and golden. Remove from pan and allow to rest for 2 minutes, then slice if preferred.
04 - If desired, lightly butter open sides of each roll. Toast cut sides face-down on the grill pan or skillet until golden brown.
05 - Spread an ample layer of basil pesto onto the base of each roll.
06 - Arrange grilled chicken, mozzarella slices, fresh tomato, and arugula or spinach atop the pesto layer. Complete with the remaining half of the bread roll.
07 - Serve assembled sandwiches warm or at room temperature.