Pat the chicken dry with paper towels—this is essential for achieving a proper blackened crust. Pound each piece to an even 1/2-inch thickness if not already done. In a small bowl, combine the cajun seasoning and garlic powder. Generously coat both sides of each chicken breast with the seasoning mixture, pressing gently so it adheres. Slice the red onion into 1/8-inch rings, slice the tomato into rounds, and tear or chop the lettuce. I like to do all my vegetable prep now so you can work quickly during the hot cooking phase.

Heat the olive oil in a large cast-iron or heavy-bottomed skillet over medium-high heat until it's shimmering and just beginning to smoke (about 2-3 minutes). Carefully place the seasoned chicken breasts in the pan—they should sizzle immediately. Cook for 5 minutes without moving them, allowing the spices to create a dark, flavorful crust. Flip each breast and cook for another 3-5 minutes until the internal temperature reaches 155°F. In the final minute of cooking, layer a slice of salami followed by a slice of provolone cheese on top of each chicken breast, allowing it to melt slightly from the residual heat.

While the chicken finishes cooking, whisk together the mayo, mustard, lemon juice, hot sauce, and smoked paprika in a small bowl until smooth and well combined. Stir in the fresh parsley for color and flavor. Once the chicken is done, transfer it to a plate and keep warm. Return the skillet (still on medium-high heat with residual oil) and place the open brioche buns cut-side down in the pan for 2-3 minutes, rotating as needed, until they're golden and lightly toasted. I always use brioche because the butter in the dough toasts beautifully and adds richness that complements the spiced chicken.

Spread a generous layer of the cajun mayo mixture on the inside of each toasted bun. Place a blackened chicken breast (with the melted salami and provolone still on top) on the bottom half of each bun. Layer lettuce, tomato slices, and red onion rings on top of the chicken in that order—this creates a nice structural foundation and allows flavors to layer properly. Top with the bun's top half and serve immediately while the chicken is still warm and the buns are toasted.