Pound the chicken breasts lightly and trim any extra fat off.

In a small bowl, stir together the Cajun seasoning, pepper, garlic powder, onion powder, and sugar.

Add 1 tablespoon of the seasoning mix to the buttermilk and stir to combine. Pour over the chicken and marinate for at least 1 hour.

Combine the remaining seasoning mix with the flour and whisk to combine.

Dip the marinated chicken into the flour mixture, pressing chunks of flour onto the chicken.

In a large heavy pan, heat vegetable oil to 350°F. Fry chicken pieces for 5-6 minutes until golden and cooked through.

Remove fried chicken and place on cooling rack. Repeat with remaining chicken.

Assemble the sandwiches by placing the fried chicken on toasted brioche buns, spreading mayonnaise, and adding pickle slices if desired.