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 small bowl until evenly coated.
03 - Heat a grill pan or skillet over medium-high heat. Cook 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 piece during the final minute of cooking. Cover briefly if needed to help the cheese melt.
05 - Butter the cut sides of the ciabatta rolls and toast them in a pan cut-side down until golden, if desired.
06 - Spread a thin layer of mayonnaise on the bottom half of each roll, then layer 1 tablespoon of basil pesto over the mayo or directly onto the bread.
07 - Layer baby spinach or arugula, sliced tomato, and the warm chicken with melted mozzarella on the bottom halves. Cap with the top halves of the rolls and serve warm.