Preheat your oven to 450°F. In a small bowl, mix the kosher salt, paprika, thyme, onion powder, garlic powder, and cayenne pepper.
Brush (or spray) the chicken breasts with oil on both sides, then sprinkle both sides with the seasoning mixture, pressing with your fingers to help the coating adhere.
Heat a well-seasoned, large cast-iron skillet over high heat until smoking hot, about 5 minutes.
Add the chicken breasts. Cook for 30 seconds on each side to blacken.
Place the skillet in the oven to finish cooking for 10-12 minutes. The chicken is done when no longer pink in the center, juices run clear when pierced with a fork, and its internal temperature reaches 165℉.
Remove the chicken to a platter, loosely cover it with foil to keep it warm, and allow it to rest for 5 minutes before slicing and serving.
