01 - Slice each chicken breast horizontally to create 4 thinner cutlets for even cooking.
02 - In a small bowl, toss the chicken cutlets with olive oil, salt, and black pepper until evenly coated.
03 - Heat a grill pan or skillet over medium-high heat. Cook the chicken for 3 to 4 minutes per side until golden brown and cooked through to an internal temperature of 165°F.
04 - During the final minute of cooking, place a slice of fresh mozzarella on top of each chicken piece and cover briefly to melt.
05 - If desired, butter the cut sides of the ciabatta rolls and toast them in a pan cut-side down 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 or directly onto the bread.
07 - Layer baby spinach or arugula, a slice of tomato, and the warm chicken with melted mozzarella on each bottom bun. Top with the remaining half of the roll and serve warm.