01 - Slice each chicken breast horizontally to create 4 thinner cutlets for even cooking.
02 - Toss chicken cutlets with olive oil, salt, and black pepper in a bowl until evenly coated.
03 - Heat a grill pan or skillet over medium-high heat. Cook chicken for 3 to 4 minutes per side until golden brown and cooked through to an internal temperature of 165°F.
04 - During the last minute of cooking, place a slice of fresh mozzarella on each chicken cutlet and cover briefly to melt.
05 - If desired, butter the cut sides of the ciabatta rolls and toast in a pan until golden.
06 - Spread a thin layer of mayonnaise on the bottom half of each roll, then layer 1 tablespoon of 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 on the sandwich and serve warm.