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