01 - Slice each chicken breast horizontally to create 4 thinner cutlets for even cooking.
02 - Toss the chicken cutlets with olive oil, salt, and black pepper in a small bowl until evenly coated.
03 - Heat a grill pan or skillet over medium-high heat. Cook the chicken cutlets for 3 to 4 minutes per side until golden brown and cooked through to an internal temperature of 165°F.
04 - Place a slice of fresh mozzarella on each chicken cutlet during the last minute of cooking and cover briefly to melt.
05 - Butter the cut sides of the ciabatta rolls and toast them in a pan cut-side down until golden.
06 - Spread a thin layer of mayonnaise on the bottom half of each roll, then spread 1 tablespoon of basil pesto over the mayo.
07 - Layer baby spinach or arugula, a slice of tomato, and the warm chicken with melted mozzarella on the bottom half of each roll.
08 - Place the top half of each roll over the layered fillings and serve immediately while warm.