Place the chicken fillets on a board and slice each one in half horizontally to give you 8 thin slices.
Put the sumac, cayenne pepper, paprika, oil and seasoning in a medium sized bowl and mix well. Add the chicken and stir to coat with the spice mixture. Set aside for a couple of minutes while you prepare the avocados and dressing.
Place the chopped avocados in a bowl and mash with a fork to a chunky paste. Stir through the lime juice, half the chilli, a little salt and pepper and set aside.
Mix the yogurt, garlic, mint and remaining chilli in a small bowl. Season with a little salt and black pepper.
Place the chicken under a hot grill or grill pan and cook for 2-3 minutes on each side or until cooked through.
Slice and toast the burger buns.
Place rocket leaves on the bun bases. Lay 2 pieces of chicken on each bun, then two slices of tomato. Spoon on some avocado then some of the yoghurt dressing.