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 cutlets 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 cutlet and cover briefly to melt.
05 - If desired, spread butter on the cut sides of the ciabatta rolls and toast them cut-side down in a pan until golden.
06 - Spread a thin layer of mayonnaise on the bottom half of each roll, then layer 1 tablespoon of basil pesto over the mayo. If skipping mayo, spread the pesto directly on the bread.
07 - Layer each roll bottom with spinach or arugula, a sliced tomato, and the warm chicken cutlet with melted mozzarella. Cap with the top half of the roll and serve warm.