Cut the thin portion of the bottom couple inches of the chicken breast off. Cut each remaining portion of the chicken breast in half then cut each of those pieces in half lengthwise. Place some saran wrap over the top of the chicken on the cutting board, and pound with a mallet until they are about a ¼-½ inch thick.
Season both sides of the chicken pieces with the blackened seasoning blend, to taste.
Heat the oil in a cast iron grill pan over medium-high heat.
Add the chicken to the hot pan and cook for 4-5 minutes, or until golden broth then flip and continue to cook for 3-4 minutes, or until cooked through.
Add the Havarti cheese slices to the top of the chicken pieces then add a teaspoon of water to the skillet and cover with a lid and cook for 1 minute to melt the cheese.
While the chicken is cooking, toast the buns in the oven until lightly golden. Remove from the oven and slather with the chipotle mayonnaise.
Top the bun with one or two pieces of chicken, followed by a thick slice of tomato and some avocado slices. Season with sea salt and freshly cracked pepper, to taste.
Top with the remaining bun and serve immediately. Enjoy.