In a small bow, stir together the chili powder, paprika, salt, black pepper cumin, garlic powder, and cayenne pepper until combined.
For grilling: Preheat grill. Brush chicken breasts with oil and then season liberally on both sides.For stove top: place a large skillet over medium-high heat. Add oil to pan and season chicken liberally on both sides.
Place chicken on hot grill/skillet. Cook for 4 to 5 minutes per side or until no longer pink in the center, flipping once.
Remove from heat and transfer to a cutting board to rest.
Cook tortillas on grill or in cleaned skillet until beginning to brown, but still flexible. (Do this for corn or flour tortillas.)
Chop or shred chicken. Mix together to help distribute seasoning to inside parts of chicken.
Add a few tablespoons of chicken along with some cheese, lettuce, tomatoes, and avocado to a taco shell. Repeat with remaining ingredients. Serve immediately.
I usually get enough chicken to make 8 tacos from 2 chicken breasts. (4 servings = 2 tacos per serving) The yield will vary if you're using thin cut breasts, and based on how big your tortillas are and how much you load them up.
Save prep time by chopping your taco toppings while the chicken is cooking.