Dredge the chicken breasts in the Cajun blackening powder so that they are well coated. In a large cast iron skillet place the 3 tablespoons of vegetable oil and heat it on high until it is very hot. Add the coated chicken breasts and fry them for 2 minutes on each side, or until they are done. Remove the chicken and slice it into diagonal strips. Set it aside. In another large skillet place the 1/4 cup of oil and heat it on medium high until it is crisp. Drain the fried tortillas on paper towels and set them aside. In a medium bowl place the lettuce and the feta cheese. Sprinkle on the Tomato Cumin Dressing and toss the ingredients together well. Spread the refried beans on each of the fried tortillas. Place the tossed lettuce, sliced chicken, and cheese on top. Garnish the tostada with 2 avocado slices.