Start by patting the chicken breasts dry with paper towels to ensure the sauce sticks well. If the breasts are very thick, use a meat mallet to pound them to an even thickness of about one inch; this helps them cook uniformly. In a small bowl, whisk together the Dijon mustard, yellow mustard, honey, olive oil, garlic powder, onion powder, smoked paprika, salt, and pepper. Reserve two tablespoons of this mixture for later. Place the chicken in a large bowl or a zip-top bag and pour the remaining marinade over it, tossing to coat every piece thoroughly. Let it sit for at least 5-10 minutes.

Preheat your air fryer to 375°F (190°C) for about 3 minutes. Lightly grease the air fryer basket with a spray of olive oil or a brush. Place the chicken breasts in the basket in a single layer, making sure they do not overlap. Cook for 12 to 15 minutes, flipping the chicken halfway through the cooking time. During the last 2 minutes of cooking, brush the reserved honey mustard sauce over the tops of the chicken breasts to create a thick, glossy glaze. Use a meat thermometer to ensure the internal temperature reaches 165°F (74°C).

Once the chicken reaches the safe internal temperature, remove it from the air fryer immediately. Transfer the chicken to a cutting board or a warm plate and tent it loosely with aluminum foil. Let the chicken rest for 5 minutes; this crucial step allows the juices to redistribute so they do not run out when you slice into it. Garnish with fresh chopped parsley if desired and serve warm with your favorite sides.