Cut the thin portion of the bottom couple of inches of the chicken breast off. Cut each remaining portion of the chicken breast in half, then cut each piece in half lengthwise.
Place plastic wrap over the top of the chicken on the cutting board, and pound with a mallet until ¼ to 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 brown. Flip and cook for 3-4 minutes, or until cooked.
Add the Havarti cheese slices to the top of the chicken pieces, then add a teaspoon of water to the skillet, 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 avocado slices. Season with sea salt and freshly cracked pepper, to taste.
Top with the remaining bun and serve immediately. Enjoy.