Mix all blackening seasoning ingredients together and set aside in a small bowl.
Brush chicken breast with 1 tablespoon of extra virgin olive oil on both sides and season both sides with blackening seasoning.
Heat remaining 1 tablespoon of oil in a skillet. Cook chicken on each side for 7 minutes. Place in preheated oven to finish cooking for 15 minutes. Allow to cool.
Dice cooled chicken and set aside, in a large bowl. To make the dressing: in a bowl, mix together mayonnaise, apple cider vinegar and Dijon mustard, set aside. Add the red onions, grated carrot and scallions to the diced chicken breast. Stir to combine. Pour dressing mix over chicken mix and stir to thoroughly combine. This can be eaten as a sandwich filling or on its own.