Sprinkle kosher salt evenly over both chicken breasts and let sit at room temperature for 15-20 minutes. This creates a quick dry brine that enhances moisture retention.

In a small bowl, whisk together Dijon mustard, honey, olive oil, apple cider vinegar, minced garlic, dried thyme, and cayenne pepper (if using) until fully incorporated into a smooth mixture.

Pat the chicken breasts dry with paper towels to remove excess moisture. Season with black pepper, garlic powder, and paprika, applying evenly to all surfaces.

Using a basting brush, thoroughly coat each chicken breast with the honey mustard mixture, ensuring complete coverage on all sides.

Set your air fryer to 380°F (193°C) and allow it to preheat for 3-5 minutes.

Place the chicken breasts in the air fryer basket, ensuring they don't overlap. Leave slight space between pieces to allow for proper air circulation.

Air fry for 6 minutes, then flip the chicken breasts using tongs. Continue cooking for another 6-8 minutes, depending on thickness.

Check the internal temperature using a meat thermometer inserted into the thickest part. The chicken is ready when it registers 165°F (74°C).

Remove the chicken from the air fryer and let rest for 5 minutes on a clean cutting board to allow juices to redistribute throughout the meat.

For optimal presentation and texture, slice against the grain before serving.