01 - Preheat grill or grill pan to medium-high heat (approximately 375°F to 400°F).
02 - Slice chicken breasts horizontally to create four thinner cutlets. Pat dry with paper towels.
03 - In a small bowl, combine olive oil, garlic powder, smoked paprika, salt, and black pepper. Rub mixture evenly over all chicken pieces.
04 - Grill chicken for 4–5 minutes per side until fully cooked, reaching an internal temperature of 165°F.
05 - During the final minute of grilling, place a cheese slice on each chicken piece. Cover grill or tent with foil for 1 minute until melted.
06 - Toast sandwich rolls on the grill or in a toaster until lightly golden and crisp.
07 - Whisk together mayonnaise, Dijon mustard, and lemon juice in a small bowl until smooth.
08 - Spread sauce on both halves of each roll. Layer with lettuce, sliced tomato, cheesy grilled chicken, and red onion. Close sandwiches and serve immediately.