In a bowl, combine buttermilk and half of the Cajun seasoning. Add chicken breasts, cover, and marinate in the refrigerator for at least 1 hour.

In a separate bowl, mix flour, paprika, garlic powder, onion powder, salt, pepper, and the remaining Cajun seasoning.

Heat vegetable oil in a deep skillet over medium-high heat to 350°F.

Remove chicken from buttermilk, allowing excess to drip off, then dredge in the flour mixture, ensuring an even coating.

Carefully place chicken in the hot oil and fry for 5-7 minutes on each side, or until golden brown and cooked through (internal temperature 165°F).

While chicken is frying, prepare the garlic aioli by mixing mayonnaise, minced garlic, lemon juice, salt, and pepper in a small bowl.

Once chicken is cooked, drain on paper towels and let rest for a few minutes.

To assemble, spread garlic aioli on the bottom half of each brioche bun, add lettuce, tomato, and the crispy chicken. Top with the other bun half and serve.