The night before you make the sandwiches, prepare the brine: In a medium bowl, combine the kosher salt, sugar, and water. Stir until completely dissolved. Place the chicken breasts in a zipper bag or covered container and pour the brine over them, ensuring the chicken is fully submerged. Seal the container and refrigerate for 12 hours.

The next day, remove the chicken from the brine and rinse under cold water to remove excess salt. Pat the chicken completely dry with paper towels.

Place each chicken breast between two sheets of plastic wrap on a cutting board. Gently pound the chicken to an even thickness of about 1/2 inch, starting from the center and working outward.

Remove the plastic wrap and place the chicken on a plate. Sprinkle the McCormick Cajun Seasoning evenly over each chicken breast, using your fingers to gently rub the spices into both sides.

Heat a large skillet over medium heat for about 2 minutes. To test if it's hot enough, sprinkle a few drops of water on the surface – they should sizzle. Spread a thin layer of softened butter on the cut sides of the brioche buns. Place the buns butter-side down in the skillet and toast until golden brown, watching carefully to prevent burning. Place the toasted buns on a plate and set aside.

In the same skillet, heat the olive oil for about 30 seconds. Carefully place the seasoned chicken breasts in the hot oil – you should hear a sizzle when the chicken touches the pan. Without moving the chicken, cook for 5 to 6 minutes on the first side, until the edges begin to turn opaque and the bottom develops a dark crust. Using tongs, carefully flip the chicken breasts over and cook for another 5 to 6 minutes on the second side. The chicken is done when a meat thermometer inserted into the thickest part reads 165°F and the center appears white throughout when cut with a knife. Transfer the cooked chicken to a plate lined with paper towels to absorb the excess oil and let rest for 2 to 3 minutes.

Spread mayonnaise on the cut sides of each bun. Arrange a layer of sliced dill pickles on the bottom half of each bun. Place a chicken breast on top of the pickles and cover with the top bun. Serve immediately while still warm.