Prep the duck: Pat the duck breasts very dry with paper towels. Use a sharp knife to score the skin in a crosshatch pattern, cutting through the fat but not into the meat. This helps render the fat and crisp the skin.
Season: Mix salt, pepper, garlic powder, smoked paprika, and rosemary.
Rub the seasoning all over, focusing on the skin side. Let the duck sit at room temperature for 15 minutes while you make the glaze.
Make the orange glaze: In a small saucepan, combine orange juice, orange zest, honey, soy sauce, vinegar, and red pepper flakes. Bring to a gentle simmer over medium heat and cook for 5–7 minutes, until slightly reduced.
If you want it thicker, stir in the cornstarch slurry and simmer 30–60 seconds more. Set aside.
Preheat the air fryer: Heat to 375°F (190°C) for 3–5 minutes. Lightly spray the basket if needed.
Cook the duck, skin side down first: Place duck breasts skin side down in the basket.
Air fry for 8 minutes. This step helps render the fat and crisp the skin without burning.
Flip and glaze: Turn the duck skin side up. Brush a thin layer of orange glaze over the top.
Air fry for another 4–7 minutes, depending on thickness, until the internal temperature reads 130–135°F (54–57°C) for medium-rare or 140°F (60°C) for medium.
Rest the duck: Transfer to a cutting board and let rest for 5–8 minutes. This keeps the juices in the meat.
Finish with glaze: Warm the remaining glaze. Slice the duck across the grain into 1/2-inch pieces.
Spoon more glaze over the top and serve.
Save the fat: Carefully pour any rendered fat from the air fryer into a heatproof jar. It’s liquid gold for roasting potatoes or sautéing vegetables.