Prep the chicken: If you’re using boneless, skinless chicken breasts and they’re large—about 8 ounces or more—slice them in half horizontally first to prevent them from becoming too large once pounded. Place each chicken breast (or half) in a 1-gallon zip-lock bag, then use a meat mallet to pound it to an even ½-inch thickness. If you’re using chicken tenderloins, simply press them to an even ½-inch thickness with the palm of your hand.
Make the spice rub: In a small bowl, mix together the salt, smoked paprika, oregano, garlic powder, onion powder, dry mustard, thyme, sugar, and cayenne pepper.
Sprinkle the chicken evenly with the spice rub. Heat the oil in a large cast iron or nonstick skillet over medium-high heat. When the oil begins to shimmer, place the chicken in the pan and cook, uncovered, for 2 to 3 minutes, until the seasoning darkens. Flip the chicken and cook for another 2 to 3 minutes, or until cooked through.