Wash and pat dry the chicken. Place each breast between two sheets of clear plastic wrap and pound until about 1/8” thick. They should flatten out to the point where you can cut each in half when cooked to make two sandwiches. Place on plate and season with 1 tablespoons of the Creole/Cajun seasoning. Set aside.
Heat a skillet over medium high heat and add 2 of the 4 tablespoons of butter. Add the onions, peppers and the remaining tablespoon of seasoning mix and sauté until onions are caramelized. Remove vegetable mixture and set aside. Add remaining butter to the skillet and sauté the chicken breast until cooked through, turning once. This may need to be done in batches.
To make chipotle mayonnaise, mix all mayonnaise ingredients together.
To assemble, spread chipotle mayonnaise mixture on both inner sides of the toasted buns then layer within the cooked chicken, sautéed onions and red bell peppers.