Preheat your oven to 400F and line a baking tray with parchment paper.
Place the chicken breasts halves between two sheets of parchment paper. Use the flat end of a meat tenderizer to flatten the chicken pieces to a ½-inch.
Prepare the crispy coating by combining in a bowl, the panko crumbs, parmesan, and 2 tablespoon of the Cajun Seasoning. Mix until well combined.
Place the flour onto a plate. In a shallow bowl, whisk together the egg and 2 tablespoon of water to make an egg wash.
Line up the bowl of coating, the plate of flour, and the bowl of egg wash.
Take 1 piece of chicken at at time with a fork. Place it in the flour to cover it on both sides. Then dip it in the egg wash, letting any excess drip off. Place in the coating mixture, lightly pressing it in so that it sticks. Cover both sides and then transfer the coated chicken to the prepared baking pan.
Lightly drizzle the coated chicken with olive oil and bake them in the preheated oven for 15 minutes, turning them over half way through. Chicken cutlets are ready when the internal temperature reaches a minimum of 165F.
Assemble the sandwiches by placing some mayonnaise and lettuce on the bottom bun, then a chicken cutlet, onion and tomato. Spread a little more mayo or burger sauce on the top bun and place it on top.