Pound the chicken breasts to an even thickness to ensure even cooking.
In a mixing bowl, combine the buttermilk with half of the salt, black pepper, and paprika. Submerge the chicken in the mixture and let it marinate for at least 30 minutes.
In a separate bowl, whisk together the flour, panko, garlic powder, cayenne pepper, and remaining seasonings.
Remove the chicken from the marinade, letting any excess drip off. Dredge each piece in the flour mixture, then dip into the beaten eggs, and finally coat with the panko-flour mix. Press firmly to ensure the coating sticks.
Preheat the air fryer to 375°F (190°C). Lightly spray the air fryer basket with oil.
Place the breaded chicken in a single layer in the air fryer basket. Cook for 12-15 minutes, flipping halfway through. Spray the chicken lightly with oil after flipping to enhance crispiness.
Check that the internal temperature reaches 165°F (74°C) before removing from the air fryer.
Toast the brioche buns if desired. Spread mayonnaise on each bun, then place the crispy chicken on top. Add pickles and any additional toppings of choice.
Serve immediately while hot for the best flavor and texture.