Pound each breast between sheets of plastic wrap to an even half-inch thickness. Combine buttermilk and hot sauce in a shallow dish, add the chicken, and turn to coat. Cover and refrigerate for at least 30 minutes, or up to 8 hours.

Whisk together the panko, flour, smoked paprika, garlic powder, cayenne, salt, and pepper in a wide bowl until no white streaks of flour remain.

Lift one breast from the buttermilk, let the excess drip off for a few seconds, then press firmly into the coating on both sides. Set on a wire rack and repeat. Mist each coated piece with a light pass of cooking spray.

Preheat the air fryer to 400°F for 3 minutes. Place breasts in a single layer — no overlapping. Cook for 7 minutes, flip carefully with a thin spatula, mist the top with cooking spray, and cook 7 more minutes. The crust should be deep golden and the internal temperature should read 165°F.

Stir together the mayo and sriracha. Toast the brioche buns cut-side down in a dry skillet for 60 seconds.

Spread spicy mayo on both bun halves. Layer the bottom with shredded lettuce, the hot crispy chicken, and pickle slices. Press the top bun down gently and serve immediately.