In a bowl, combine buttermilk and 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, and pepper well.

Heat vegetable oil in a deep skillet over medium-high heat (aim for about 350°F).

Remove chicken from the buttermilk, letting excess drip off, and dredge in the flour mixture, ensuring even coverage.

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

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

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

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