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