Pound the chicken breasts to an even thickness.
In a bowl, mix buttermilk with salt and pepper. Add chicken and marinate for 30 minutes.
In a separate bowl, mix flour, breadcrumbs, garlic powder, onion powder, paprika, salt, and pepper.
Dredge the chicken in the flour mixture until fully coated.
Heat oil in a pan over medium-high heat. Fry chicken until golden and crispy, about 4 minutes per side.
In a small bowl, mix Caesar dressing, mayonnaise, and lemon juice.
Toast the brioche buns lightly.
Assemble the sandwich: Spread Caesar dressing mixture on the buns, place crispy chicken, top with shredded lettuce and Parmesan cheese.
Serve immediately and enjoy!