01 - Slice each chicken breast horizontally to create 4 thinner cutlets of even thickness.
02 - Toss the chicken cutlets in a bowl with olive oil, salt, and black pepper until evenly coated.
03 - Heat a grill pan or skillet over medium-high heat. Cook the 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 cutlet during the final minute of cooking and cover briefly to melt.
05 - Butter the cut sides of the ciabatta rolls and toast them in a pan until golden and crisp.
06 - Spread a thin layer of mayonnaise on the bottom half of each roll, then layer 1 tablespoon of basil pesto over the mayo.
07 - Layer baby spinach or arugula and sliced tomato on the bottom halves, then place the warm chicken with melted mozzarella on top.
08 - Cap each sandwich with the top half of the roll and serve immediately while warm.