Optional brine (2–6 hrs): In a large bowl, dissolve ¼ cup kosher salt + ¼ cup sugar in 4 cups cold water. Add turkey breast, cover, and refrigerate 2–6 hours. Rinse and pat dry.
Preheat air fryer: Preheat to 360°F (182°C) for 3–5 minutes.
Make herb butter: Mix 3 tbsp softened butter, minced garlic, rosemary, thyme, smoked paprika, salt, pepper, and lemon zest.
Apply butter: Gently loosen skin and spread 2 tbsp herb butter under the skin; rub remaining butter over the skin.
Place in basket: Put breast skin-side up in the air fryer basket with space around it. Lightly spray with oil.
Air fry:
3 lb bone-in: Air fry 360°F (182°C) for 45–55 minutes.
2–2.5 lb boneless: Air fry 360°F (182°C) for 30–40 minutes.
Use an instant-read thermometer to check the thickest point.
Finish (optional): If needed for color, increase to 400°F (204°C) for the last 3–5 minutes.
Target temp & rest: Remove when the internal temp reads 160°F (71°C); tent with foil and rest 10–15 minutes (carryover heat will reach 165°F / 74°C). If you prefer, you can wait until it registers 165°F (74°C) before removing.
Slice & serve: Slice against the grain and serve with pan juices or gravy.